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Mother-to-child transmission of HIV-1 and infant mortality in the first six months of life, in the era of Option B Plus combination antiretroviral therapy

Open AccessPublished:June 20, 2021DOI:https://doi.org/10.1016/j.ijid.2021.06.036

      Highlights

      • Mother-to-child transmission of HIV occurs intrauterine, intrapartum, and postpartum.
      • Intrauterine is the major route of mother-to-child transmission of HIV.
      • Option B Plus combination antiretroviral therapy reduces mother-to-child transmission of HIV.
      • Death occurred only among the HIV-uninfected infants.

      Abstract

      Objectives

      The aim of this study was to determine the contributions of intrauterine (IU), intrapartum (IP), and postpartum (PP) transmission to mother-to-child transmission of HIV-1 (MTCT) and infant mortality in the first 6 months of life, in the era of Option B Plus combination antiretroviral therapy.

      Methods

      Plasma for virus load (VL) quantitation was obtained from 451 women enrolled into the study. VL was quantified using the Cepheid GeneXpert HIV-1 quantitative test. Dried blood spots were collected from 453 infants at birth, 4–6 weeks, 3 months, and 6 months. HIV-1 infant diagnosis was conducted using the Cepheid GeneXpert HIV-1 qualitative test. Absolute and cumulative MTCT rates, and the mortality rate by 6 months were calculated.

      Results

      Seven mothers (1.55%) had transmitted HIV-1 infection to their infants by 6 months. Four infants (0.88%, 95% confidence interval (CI) 0.26–2.33%) were infected IU, one infant (0.22%, 95% CI 0–1.4%) was infected IP, and two infants (0.44%, 95% CI 0.01–1.7%) were infected PP. The infant mortality rate was 0.88% (95% CI 0.26–2.33%).

      Conclusions

      In the first 6 months of life, in the era of Option B Plus combination antiretroviral therapy, IU transmission is the major route of MTCT. The cumulative MTCT rate of 1.55% in a breastfeeding population contributes to growing evidence that complete elimination of MTCT is possible.

      KEYWORDS

      1. Introduction

      Mother-to-child transmission of HIV-1 (MTCT) can occur intrauterine (IU), or intrapartum (IP), or postpartum (PP) mainly via breastfeeding. Characterizing the three modes of HIV-1 transmission is important, as different risk factors may influence transmission during each period (
      • Zijenah LS
      • Moulton LH
      • Iliff P
      • Nathoo K
      • Munjoma MW
      • Mutasa K
      • et al.
      Timing of mother-to-child transmission of HIV-1 and infant mortality in the first 6 months of life in Harare.
      ) and thus different modalities may be required for their prevention. Furthermore, characterizing the timing of MTCT may lead to a better understanding of the biological mechanisms of HIV-1 transmission, as well as the epidemiology and pathogenesis of HIV infection, which may be utilized in designing and evaluating interventions to reduce MTCT.
      In 2013, the World Health Organization (WHO) recommended that all HIV-infected pregnant women should be commenced on combination antiretroviral therapy (cART) for life, regardless of their CD4 count – dubbed Option B Plus cART – for the treatment of maternal HIV infection/disease and prevention of MTCT (PMTCT), with all infants born to HIV-infected mothers receiving nevirapine prophylaxis for the first 6 weeks of life and exclusive breastfeeding for the first 6 months of life (

      World Health Organization. Consolidated guidelines on the use of antiretroviral drugs for treating and preventing HIV infection. 2013. Accessed 04 January 2021, Available from: https://www.who.int/hiv/pub/guidelines/arv2013/download/en/.

      ).
      Following the WHO recommendations (

      World Health Organization. Consolidated guidelines on the use of antiretroviral drugs for treating and preventing HIV infection. 2013. Accessed 04 January 2021, Available from: https://www.who.int/hiv/pub/guidelines/arv2013/download/en/.

      ), most low- and middle-income countries have incorporated Option B Plus in their national PMTCT programmes (

      World Health Organization. Global health sector response to HIV, 2000-2015: focus on innovations in Africa: progress report. Accessed on 26 May 2021. Available from: http://apps.who.int/iris/bitstream/10665/198065/1/9789241509824_eng.pdf?ua=1

      ). Some studies have reported overall cumulative rates of MTCT following the implementation of Option B Plus (

      UNAIDS. Global aids update 2018, Miles to go closing gaps breaking barriers righting injustice. Accessed on 26 May 2021. Available from: https://www.unaids.org/sites/default/files/media_asset/miles-to-go_en.pdf ].

      ). We are not aware of any study in Africa or globally that has examined the contributions of the three modes of MTCT, namely intrauterine, intrapartum, and postpartum, to MTCT.
      Zimbabwe adopted the Option B Plus PMTCT programme in 2014. This study was conducted at a primary healthcare clinic to determine the contributions of IU, IP, and PP MTCT in the first 6 months of life, in the era of Option B Plus.

      2. Methods

      The study was conducted at Mabvuku Polyclinic, a primary health care centre. Mabvuku is a high-density suburb of Harare, the capital city of Zimbabwe, and is 20 km from the city centre. It has a catchment population of 110 438 people. The clinic has a laboratory on site, where a four-module GeneXpert machine for the diagnosis of HIV-1 infection and viral load (VL) quantitation, a desktop computer, an uninterrupted power supply, and a biosafety cabinet were installed for this study.
      HIV-infected pregnant women at various stages of gestation who had registered for antenatal clinic services at Mabvuku Polyclinic were enrolled into the parent study, titled “Optimization of Option B+ for PMTCT of HIV through implementation of point-of-care maternal HIV load, early infant diagnosis (POCOBART Study)”. The study was approved by the Medical Research Council of Zimbabwe (MRCZ/A/2113). Before enrolment, study procedures were discussed with the women and a written informed consent agreement was signed by the women who voluntarily consented to enrolling themselves and their unborn babies into the study. The POCOBART study was designed to optimize Option B Plus for PMTCT by offering VL quantitation at enrolment and every 6 months thereafter, not currently offered by the clinic. Women with VL measurements >1000 copies/ml had VL quantitation repeated within 2 weeks. Those with a VL >1000 copies/ml in two consecutive tests were referred to the clinic for consideration of switching to an alternative cART regimen if they were suspected to have developed drug resistance but with confirmed good adherence to cART. Infants born to the women were tested at birth, 4–6 weeks, and every 3 months thereafter. Infants who tested positive for HIV-1 were referred to the clinic for consideration of cART commencement. Those infants initiated on cART were then followed up every 6 months with VL quantified as for their mothers, in order to monitor their virological response to cART. Under the Zimbabwe National PMTCT programme, diagnosis of infant HIV infection is not conducted at the clinic, but dried blood spots are collected at 4–6 weeks postnatally and sent to the centralized laboratory for diagnosis of infant HIV infection.

      2.1 Viral load quantitation

      Whole blood in EDTA was collected and centrifuged within 6 hours of phlebotomy to obtain plasma for VL quantitation. VL quantitation was conducted at enrolment for the mothers and every 6 months thereafter, using the point-of-care (POC) Cepheid GeneXpert HIV-1 quantitative test (Cepheid, Sunnyvale, CA, USA), following the manufacturer's instructions. VL quantitation was repeated within 2 weeks for those with a VL >1000 copies/ml. The test is semi-automated and at the end of the run, results are reported as HIV-1 detected with the number of viral copies displayed, or as HIV-1 undetected for participants with a VL <20 copies/ml (the lower detection limit of the assay), or as invalid or error or no result. A retest was done using a new cartridge and new reagents if an error or invalid test or no result was reported.

      2.2 Diagnosis of infant HIV infection

      From the infants enrolled into the study, aliquots of 50 µl of finger-prick blood were collected (five spots per card, using No. 903 Protein Saver cards; Whatman), at birth, 4–6 weeks, and every 3 months thereafter. These were air dried and used for POC early HIV infection diagnosis (EID). The POC Cepheid GeneXpert HIV-1 qualitative test (Cepheid, Sunnyvale, CA, USA) was employed for EID. Results were interpreted automatically and displayed as positive or negative or invalid or error or no result. A retest was done using a new cartridge and new reagents if an error or invalid test or no result occurred. The infants who were diagnosed with HIV infection were immediately referred to the clinic for consideration of immediate cART commencement.

      2.3 Timing of infant HIV infection

      The timing of IU infection was defined as infants testing HIV-positive at birth. Infants who tested HIV-1-negative at birth but subsequently tested HIV-positive at 4–6 weeks were considered to have evidence of IP infection. PP infection was defined as infants who tested HIV-negative at birth and at 4–6 weeks, and subsequently tested first HIV-positive at 3 months or later (
      • Bertolli J
      • St Louis ME
      • Simmonds RJ
      • Nieburg P
      • Kamenga M
      • Brown C
      • et al.
      Estimating the timing of mother to child transmission of human immunodeficiency virus in a breastfeeding population in Kinshasa.
      ;
      • Bryson YJ
      • Luzuriaga K
      • Sullivan JL
      • Wara DW.
      Proposed definition for in utero versus intrapartum transmission of HIV-1.
      ;
      • Zijenah LS
      • Moulton LH
      • Iliff P
      • Nathoo K
      • Munjoma MW
      • Mutasa K
      • et al.
      Timing of mother-to-child transmission of HIV-1 and infant mortality in the first 6 months of life in Harare.
      ).

      2.4 Statistical analysis

      Baseline characteristics of the HIV-infected pregnant women on cART are described in relation to their clinical characteristics. Summary statistics for categorical variables are presented as frequencies and percentages, and for continuous variables as the mean and standard deviation or non-parametric median and interquartile range (IQR). Timing of cART commencement was extracted from the mothers’ clinical records. Duration on cART was calculated from the date the mother commenced cART to the date the mother was enrolled into the study. Rates of mode of transmission, cumulative mortality, and overall MTCT at 6 months were calculated. All mothers and infant pairs lost to follow-up or who withdrew from the study were not included in the analysis. All analyses were performed using Stata release 15 (StataCorp, College Station, TX, USA).

      3. Results

      A total of 502 women were enrolled into the study between December 6, 2017 and December 31, 2018. Sixteen (16) women had foetal losses (6 spontaneous abortions and 10 stillbirths). There were 492 live births, including six twin sets. Twelve babies died before they were enrolled into the study. The cause of death in 9/12 (75%) of the babies who died before enrolment was respiratory distress; two babies (2/12, 16.7%) died from birth asphyxia and one baby (1/12, 8.3%) died from biliary obstruction. Twenty-seven infants were withdrawn from the study by either their mother or father or both after delivery. Thus, 453 infants including two twin sets and two single twins were enrolled into the study and each was followed-up for 6 months (Figure 1, Figure 2).
      Figure 1
      Figure 1Enrolment of women and their babies. The figure shows the number of mothers enrolled into the study and pregnancy outcomes, as well as the number of babies who were excluded from the study and those who were enrolled into the study.
      Figure 2
      Figure 2Flow chart of HIV testing of enrolled infants and outcomes. The figure shows HIV testing of the enrolled infants at birth, 4–6 weeks, 3 months, and 6 months, as well as the outcomes of testing at each visit.

      3.1 Baseline characteristics of HIV-infected pregnant women who transmitted HIV infection to their infants (transmitters) and those who did not (non-transmitters)

      Table 1 reports the baseline characteristics of the transmitters and non-transmitters. The small number of transmitters (n = 7) compared to non-transmitters (n = 444) was considered not adequate to provide credible statistical inference on differences between the two groups. The mean age of the transmitters and non-transmitters was just above 30 years. The majority of both the transmitters (100%) and non-transmitters (51.13%) were in their third trimester, with a median gestational period of 29 weeks (IQR 23–34 weeks), when they were enrolled in the study. Overall, their body mass index (BMI) was within the normal range for pregnant women. The majority of the women, 434/451 (96.23%), were on the first-line cART regimen tenofovir/lamivudine/efavirenz. cART was initiated before conception in 60.31% of women, during the first trimester in 3.77%, during the second trimester in 23.50%, and during the third trimester in 12.42%. The median duration on current cART of the transmitters was 0.02 years (IQR 0–0.22 years), compared to 1.80 years (IQR 0.10–3.55 years) for the non-transmitters.
      Table 1Baseline characteristics at enrolment into the study of HIV-infected pregnant women who transmitted (transmitters) and those who did not transmit (non-transmitters) HIV infection to their infants
      Transmitters(n = 7), n (%)Non-transmitters (n = 444), n (%)All (n = 451), n (%)
      Maternal characteristics
      Age (years)Mean ± SD30.47 ± 8.9530.37 ± 6.3130.36 ± 6.35
      cART regimen
      ABC, abacavir; 3TC, lamivudine; ATV, atazanavir; AZT, zidovudine; ATV/R, atazanavir/ritonavir; D4T, stavudine; NVP, nevirapine; DTG, dolutegravir; TAF, tenofovir alafenamide, TDF, tenofovir fumarate; EFV, efavirenz.
      ABC/3TC/ATV0 (0.00)1 (0.23)1 (0.22)
      AZT/ 3TC/ATV/R0 (0.00)7 (1.58)7 (1.55)
      D4T/3TC/NVP0 (0.00)2 (0.45)2 (0.44)
      DTG/FTC/TAF0 (0.00)1 (0.23)1 (0.22)
      TDF/3TC/NVP1 (14.29)5 (1.13)6 (1.33)
      TDF/3TC/EFV6 (85.71)428 (96.40)434 (96.23)
      Timing of cART initiation as reported at enrolment into the study
      Preconception1 (14.29)271 (61.04)272 (60.31)
      During pregnancy
        1st trimester≤12 weeks0 (0.00)17 (3.83)17 (3.77)
        2nd trimester13–28 weeks2 (28.57)104 (23.42)106 (23.50)
        3rd trimester29–40 weeks4 (57.14)52 (11.71)56 (12.42)
      Duration on current cART (years)
      Duration on cART (years) was calculated from the date cART was commenced up to the date the mother was enrolled into the study.
      ≤0.56 (85.71)175 (39.41)181 (40.13)
      >0.51 (14.29)269 (60.59)270 (59.87)
      Median (IQR)0.02 (0–0.22)1.80 (0.10–3.55)1.70 (0.10–3.50)
      BMI (kg/m2)
        Underweight≤18.50 (0.00)20 (4.50)20 (4.43)
        Normal weight18.6–24.92 (28.57)232 (52.25)234 (51.88)
        Overweight25–29.93 (42.86)133 (29.95)136 (30.16)
        Obese≥302 (28.57)59 (13.29)61 (13.53)
      Gestational period (weeks)
        1st trimester≤120 (0.00)8 (1.80)8 (1.77)
        2nd trimester13–280 (0.00)209 (47.07)209 (46.34)
        3rd trimester29–407 (100)227 (51.13)234 (51.88)
      Median (IQR)34 (32–37)29 (23–33)29 (23–34)
      Viral load (copies/ml)<200 (0.00)278 (62.61)278 (61.64)
      20–9990 (0.00)56 (12.61)56 (12.42)
      ≥10007 (100.00)110 (24.77)117 (25.94)
      Viral load (log10/ml)Median (IQR)4.91 (3.62–5.31)1 (1–2.93)1 (1–3.17)
      cART, combination antiretroviral therapy; SD, standard deviation; IQR, interquartile range; BMI, body mass index.
      a ABC, abacavir; 3TC, lamivudine; ATV, atazanavir; AZT, zidovudine; ATV/R, atazanavir/ritonavir; D4T, stavudine; NVP, nevirapine; DTG, dolutegravir; TAF, tenofovir alafenamide, TDF, tenofovir fumarate; EFV, efavirenz.
      b Duration on cART (years) was calculated from the date cART was commenced up to the date the mother was enrolled into the study.
      Whilst all seven transmitters had a detectable VL (>1000 copies/ml), the majority of the non-transmitters, 278/444 (62.61%), had an undetectable VL (<20 copies/ml).

      3.2 Timing of HIV-1 infections

      Figure 2 shows the HIV testing of the enrolled infants at birth, 4–6 weeks, 3 months, and 6 months and the outcomes. Seven infants were infected by 6 months. The estimated cumulative MTCT rate at 6 months based on the seven HIV-infected infants (7/453) was 1.55% (95% confidence interval (CI) 0.68–3.22%). Four of the infected infants were HIV-1-positive at birth suggesting IU infection. The IU transmission rate was 0.88% (95% CI 0.26–2.33%). The fifth infant tested HIV-1-negative at birth and subsequently first tested HIV-1-positive at the 4–6 weeks follow-up visit, implying an IP transmission rate of 0.22% (95% CI 0–1.4%). The sixth infant tested HIV-1-negative at birth and at the 4–6 weeks follow-up visit, but subsequently first tested HIV-1-positive at 3 months, and the seventh infant was HIV-1-negative at birth, 4–6 weeks, and 3 months, but subsequently first tested HIV-1-positive at 6 months. These two infants were classified as having PP transmission. The PP transmission rate was 0.44% (95% CI 0.01–1.7%).

      3.3 Characteristics of HIV-positive and HIV-negative infants

      The characteristics of the HIV-positive and HIV-negative infants are shown in Table 2. More than half of the infants were male (53.42%). The majority of the infants in both the HIV-positive and HIV-negative groups had weights above the 2.5 kg cut-off for low birth weight in Zimbabwe. All of the infants in the two groups except one set of twins in the HIV-negative group (the mother was not able to produce sufficient breast milk for the twins) were exclusively breastfed in the first 6 months of life. The majority of the infants in both groups (100% in the HIV-infected group and 90.58% in the HIV-negative group) were from vaginal deliveries.
      Table 2Characteristics of the HIV-positive and HIV-negative infants and mortality at 6 months
      Infant characteristicsHIV-positive (n = 7), n (%)HIV-negative (n = 446), n (%)All (n = 453), n (%)
      SexFemale3 (42.86)208 (46.64)211 (46.58)
      Male4 (57.14)238 (53.36)242 (53.42)
      Weight (kg)
        Low birth weight≤2.51 (14.29)52 (11.66)53 (11.70)
        Normal birth weight>2.56 (85.71)394 (88.34)400 (88.30)
      Mode of feedingExclusive breast7 (100.00)444 (99.55)451 (99.56)
      Breast and other0 (0.00)2 (0.45)2 (0.44)
      Dead by 6 monthsYes0 (0.00)4 (0.90)4 (0.88)
      No7 (100.00)442 (99.10)449 (99.12)
      Mode of deliveryVaginal7 (100.00)404 (90.58)411 (90.73)
      C-section0 (0.00)42 (9.42)42 (9.27)

      3.4 Baseline characteristics of mothers who transmitted HIV infection to their infants

      Table 3 shows the characteristics of the seven transmitters. The small numbers of IU (n = 4), IP (n = 1), and PP (n = 2) transmitters were considered not adequate to conduct any statistically meaningful comparisons of the three groups, neither was it possible to perform any analysis to identify the risk factors associated with the three modes of transmission. All of the mothers who transmitted HIV-1 infection to their infants (transmitters) were over the age of 20 years, their ages varying from 22 to 43 years. They were all in the third trimester of their pregnancy when they were enrolled into the study. All but one had been on cART for less than 6 months and all had a detectable VL (>1000 copies/ml). The only mother (mother 2) who had been on cART for 5.92 years was on third-line cART, whilst the remainder were on their first-line cART regimen. Interestingly, the woman with the highest VL at enrolment (mother 7), log10 6.50 copies/ml, did not transmit HIV infection to her infant IU or IP, but at 6 months postpartum. All seven of the mothers exclusively breastfed their infants.
      Table 3Baseline characteristics of mothers who transmitted HIV-1 to their infants (transmitters).
      IntrauterineIntrapartumPostpartum
      Number1234567
      Age (years)20324340242230
      cART regimenTDF/3TC/EFVTDF/3TC/NVPTDF/3TC/EFVTDF/3TC/EFVTDF/3TC/EFVTDF/3TC/EFVTDF/3TC/EFV
      Duration on cART (years)0.225.920.020.2000.020
      BMI (kg/m2)26.735.825.931.624.620.625.1
      Gestation period (weeks)37343432303538
      VL (log10 copies/ml)5.233.623.445.314.913.926.53
      cART, combination antiretroviral therapy; BMI, body mass index; VL, viral load; TDF, tenofovir fumarate; 3TC, lamivudine; EFV, efavirenz; NVP, nevirapine.

      3.5 Mortality of infants

      Four of the 453 live born infants died within the first 6 months of life (Table 2), giving an estimated mortality rate of 0.88% (95% CI 0.26–2.33%). All four of the infants tested HIV-1-negative at their last scheduled clinic visit before they died. The cause of death for the first infant who died whilst sleeping aged 1 month and 10 days after testing HIV-negative at birth and at 4 weeks is unknown. The second infant who tested HIV-1-negative at birth and at 4–6 weeks died of respiratory asphyxia at the age of 2 months. The third infant who tested HIV-negative at birth, at 4–6 weeks, and at 3 months died of pneumonia aged 3 months and 3 weeks. The fourth infant born with hydrocephalus died of an unknown cause aged 5 months having tested HIV-negative at birth, at 4–6 weeks, and at 3 months.

      4. Discussion

      This study, conducted at a primary health clinic, is the first in Zimbabwe to report on the timing of MTCT in the era of Option B Plus cART for PMTCT. We are not aware of any study globally that has investigated the contributions of IU, IP, and PP MTCT transmission rates in the era of Option B Plus. These three modes of HIV-1 transmission are important, as different modalities may be required for their prevention, particularly in developing countries with limited financial resources.
      This study showed that the majority of MTCT in the era of Option B Plus, assessed in the first 6 months of life, occurs IU. This is a cause for concern as in Zimbabwe and indeed in many other developing countries, the diagnosis of HIV-1 infection in infants born to HIV-infected women starts at 4–6 weeks postnatally. The time point of 4–6 weeks was selected to coincide with the infants’ first immunization clinic visit and additionally because of the financial constraints to conduct EID at birth. However, the delayed EID will lead to delayed commencement of cART for the IU HIV-infected infants with a consequent mortality risk, which begins to increase at about 3–4 weeks of age and may be as high as 10% by age 2 months for infants with IU or IP transmission (
      • Bourne DE
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      Emergence of a peak in early infant mortality due to HIV/AIDS in South Africa.
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      ).
      The overall 6-month MTCT rate of 1.55% observed in the current study is within the reported rates of 1–2% for HIV-infected non-breastfeeding women who are on cART in the developed countries (

      UNAIDS, Ending AIDS: progress towards the 90-90-90 targets. Global AIDS update, 2017. Accessed 21 January 2021. Available from: https://www.aidsdatahub.org/resource/ending-aids-progress-towards-90-90-90-targets-global-aids-update-2017.

      ). Prior to the introduction of cART for PMTCT, the rate of MTCT in early 2000 was 30.7% in breastfeeding Zimbabweans (
      • Zijenah LS
      • Moulton LH
      • Iliff P
      • Nathoo K
      • Munjoma MW
      • Mutasa K
      • et al.
      Timing of mother-to-child transmission of HIV-1 and infant mortality in the first 6 months of life in Harare.
      ). The IU transmission (defined as HIV-positive within 96 hours of birth) rate was 9.4%, the early IP/late PP transmission (defined as first positive at 6 weeks) rate was 16.4%, and the late PP transmission (defined as negative at birth and 6 weeks and first positive at an older age) rate was 5.3%. In sharp contrast, in the current study of Option B Plus for PMTCT, the IU transmission rate was 0.88%, the IP transmission rate was 0.22%, and the PP transmission rate was 0.44%. The IU rate in the current study is comparable to the 0.80% and 0.91% for HIV-infected women in Botswana, who commenced dolutegravir/tenofovir/emtricitabine and efavirenz/tenofovir/emtricitabine cART regimens, respectively, during pregnancy (
      • Davey S
      • Ajibola G
      • Maswabi K
      • Sakoi M
      • Bennett K
      • Hughes MD
      • et al.
      Mother-to-child HIV transmission with in Utero Dolutegravir vs. Efavirenz in Botswana.
      ). The Botswana study reported only IU transmission rates.
      Six of the seven transmitters were in their third trimester, had been on cART for less than 6 months when they were enrolled into the study, and were viraemic. The seventh transmitter who had been on cART for more than 5 years was also viraemic and on a third-line cART regimen. Surprisingly, there was also a small proportion (24.77%) of women in their third trimester who had been on cART for less than 6 months, were viraemic at enrolment, but did not transmit HIV-1 to their infants. Recent studies in the era of cART have reported children being infected despite the use of antiretroviral regimens for PMTCT (
      • Violari A
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      ). Previous studies conducted in the pre-cART for PMTCT era identified high VL as a risk factor for MTCT (
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      ). All of the transmitters in the current study had a detectable VL at enrolment. It is plausible that the transmitters had already transmitted HIV-1 to their foetuses/infants prior to the commencement of cART. Thus, early initiation of cART by HIV-infected pregnant women may be key to the prevention of IU MTCT. Ideally, all women of reproductive age should be tested for HIV infection and those who are HIV-infected commenced on cART and ensured to have an undetectable VL before conception. Indeed, a study conducted in France reported zero MTCT in HIV-infected women who were on cART with an undetectable VL before conception and who continued cART throughout pregnancy and had an undetectable VL at delivery (
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      ).
      Prior to the introduction of cART for PMTCT, one-third to one-half of PP transmission in sub-Saharan Africa was attributable to breastfeeding (
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      • et al.
      Postnatal transmission of human immunodeficiency virus type 1 from mother to infant: a prospective cohort study in Kigali, Rwanda.
      ). Breastfeeding, mostly in the form of mixed feeding, is widely practised in sub-Saharan Africa. In the early years of the HIV/AIDS epidemic, observational data from a randomised clinical trial of antenatal vitamin A supplementation to assess its impact on MTCT reported a lower risk of postnatal HIV transmission in exclusively breastfed infants than in infants who had mixed breastfeeding (
      • Coutsoudis A
      • Pillay K
      • Spooner E
      • Kuhn L
      • Coovadia HM
      for the South African Vitamin A Study Group
      Influence of infant-feeding patterns on early mother-to-child transmission of HIV-1 in Durban, South Africa: a prospective cohort study.
      ). Another randomized clinical trial of a vitamin A supplementation targeted at reducing MTCT reported lower PP transmission risk and mortality in exclusively breastfed infants compared to infants who received mixed feeding (
      • Iliff PJ
      • Piwoz EG
      • Tavengwa NV
      • Zunguza CD
      • Marinda ET
      • Nathoo KJ
      • et al.
      Early exclusive breastfeeding reduces the risk of postnatal HIV-1 transmission and increases HIV-free survival.
      ). In the era of single-dose nevirapine for PMTCT, a non-randomized observational study in which pregnant mothers were given single-dose nevirapine at 28 weeks of gestation, with mothers voluntarily opting to exclusively breastfeed or use replacement feeding (breastmilk and other foods) during the first 6 months of life, reported a lower MTCT risk and mortality in exclusively breastfed infants compared to infants on replacement feeding (
      • Coovadia HM
      • Rollins NC
      • Bland RM
      • Little K
      • Coutsoudis A
      • Bennish ML
      • et al.
      Mother-to-child transmission of HIV-1 infection during exclusive breastfeeding in the first 6 months of life: an intervention cohort study.
      ). Several studies using short-course antiretroviral regimens given to either the mother or infant during breastfeeding reduced the PP transmission rate (
      • Bedri A
      • Gudetta B
      • Isehak A
      • Kumbi S
      • Lulseged S
      • Mengistu Y
      • et al.
      Extended-dose nevirapine to 6 weeks of age for infants to prevent HIV transmission via breastfeeding in Ethiopia, India, and Uganda: an analysis of three randomised controlled trials.
      ;
      • Chasela CS
      • Hudgens MG
      • Jamieson DJ
      • Kayira D
      • Hosseinipour MC
      • Kourtis AP
      • et al.
      Maternal or infant antiretroviral drugs to reduce HIV-1 transmission.
      ;
      • Kilewo C
      • Karlsson K
      • Ngarina M
      • Massawe A
      • Lyamuya E
      • Swai A
      • et al.
      Prevention of mother-to-child transmission of HIV-1 through breastfeeding by treating mothers with triple antiretroviral therapy in Dar es Salaam, Tanzania: the Mitra plus study.
      ;
      • Kumwenda NI
      • Hoover DR
      • Mofenson LM
      • Thigpen MC
      • Kafulafula G
      • Li Q
      • et al.
      Extended antiretroviral prophylaxis to reduce breast-milk HIV-1 transmission.
      ;
      • Shapiro RL
      • Hughes MD
      • Ogwu A
      • Kitch D
      • Lockman S
      • Moffat C
      • et al.
      Antiretroviral regimens in pregnancy and breast-feeding in Botswana.
      ;
      • Thomas TK
      • Masaba R
      • Borkowf CB
      • Ndivo R
      • Zeh C
      • Misore A
      • et al.
      Triple-antiretroviral prophylaxis to prevent mother-to-child HIV transmission through breastfeeding-the Kisumu Breastfeeding Study, Kenya: a clinical trial.
      ;
      • Wiktor SZ
      • Ekpini E
      • Karon JM
      • Nkengasong J
      • Maurice C
      • Severin ST
      • et al.
      Short-course oral zidovudine for prevention of mother-to-child transmission of HIV-1 in Abidjan, Cote d'Ivoire: a randomised trial.
      ). These and several earlier studies targeted at reducing MTCT in developing countries eventually culminated in the WHO recommendation of Option B Plus for PMTCT and treatment of maternal HIV infection/disease.
      All but one mother in the current study exclusively breastfed in the first 6 months of life. All of their infants were on nevirapine prophylaxis for the first 6 weeks of life. The PP transmission rate of 0.44% in the present study appears to indicate that the risk of PP transmission through breastfeeding can be reduced if the mothers are on cART, virologically suppressed, and exclusively breastfeed during the first 6 months. The impact of introducing mixed feeding after 6 months of exclusive breastfeeding on the PP transmission rate remains to be elucidated at the end of the 2-year follow-up of the infants in the current ongoing study.
      The mortality rate of 0.88% at 6 months in the current study is in sharp contrast to the 11.8% in the absence of any intervention for infants born to HIV-1-infected mothers, with the majority (69%) of the infants who died being HIV-1-positive in the first 6 months of life (
      • Zijenah LS
      • Moulton LH
      • Iliff P
      • Nathoo K
      • Munjoma MW
      • Mutasa K
      • et al.
      Timing of mother-to-child transmission of HIV-1 and infant mortality in the first 6 months of life in Harare.
      ). Intriguingly, in the current study, all four of the infants who died tested HIV-1-negative at the last clinic scheduled visit before they died. Option B Plus cART appears not to only drastically reduce the risk of MTCT but also infant mortality.
      This study has a few limitations and some strengths. The IU transmission rate and the overall MTCT rate may have been underestimated. The HIV infection status of the 12 live born babies who died before enrolment was not known. Furthermore, the HIV infection status of the 27 babies withdrawn from the study at birth before being HIV-tested was also not known; however all of their mothers had an undetectable VL at enrolment into the study, thus possibly reducing the chances of transmitting HIV-1 to their infants if they continued taking their antiretroviral drugs throughout pregnancy. The major reason for withdrawal of the mothers and their infants from continued participation in the study was relocation from the study area to other parts of the country or outside the country.
      Mabvuku Polyclinic does not offer onsite diagnosis of infant HIV infection or VL quantitation for monitoring the response to cART. In so far as EID of HIV infection is concerned, the clinic collects dried blood spots at 4–6 weeks (thus missing HIV testing at birth) and sends them to the centralized laboratory for EID of HIV infection. The major strength of this study is that we have shown that it is possible to conduct POC EID of HIV infection, starting at birth, and to monitor the response to cART by quantitating VL at a primary healthcare clinic. Mabvuku Polyclinic has a Cepheid GeneXpert machine purchased for the diagnosis of Mycobacterium tuberculosis; the same machine can be utilized for EID of HIV infection and for monitoring the response to cART onsite.
      In conclusion, in the first 6 months of life, in the era of Option B Plus cART, IU transmission is the major route of MTCT. The cumulative MTCT rate of 1.55% in a breastfeeding population contributes to growing evidence that complete elimination of MTCT is possible.

      Author contributions

      L.S.Z. and D.A.K* made substantial contributions to the conception and design of the study. L.S.Z., M.M.C., W.B. and T.B. contributed substantially to acquisition of the data. L.S.Z., T.B., M.M.C., W.B. and D.A.K contributed substantially to the data analysis. L.S.Z. prepared the manuscript. L.S.Z., T.B., M.M.C., W.B. and D.A.K. revised the manuscript critically for important intellectual content. L.S.Z., T.B., M.M.C. and W.B. gave final approval of the submitted version of the manuscript.

      Conflict of interest

      None of the authors have a financial or personal relationship with other people or organizations that could inappropriately influence (bias) their work.

      Acknowledgements

      We thank the study participants and their families and the Mabvuku Polyclinic staff. We also thank Maureen C.F. Sahanga, Janice Martin, and Tafadzwa D. Nyakubaya for conducting the laboratory tests, and Brian Nyauzame and Mutsa R.J. Makunike for data capture.

      Funding

      This study is part of the EDCTP2 programme supported by the European Union (grant number 1051 TESA II EDCTP-RegNet2015). The funder was not involved in the study design, collection, analysis and interpretation of the data, writing of the report, or the decision to submit the article for publication.

      Ethics statement

      The study was approved by the Medical Research Council of Zimbabwe (MRCZ/A/2113). Written informed consent was obtained from all study participants.

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