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High ratio of measles-specific IgG/IgM associated with nodular pneumonia in vaccinated individuals

  • Author Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    Donghao Yu
    Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    Affiliations
    Beijing Chaoyang Hospital of Capital Medical University, Beijing, China

    Department of Pulmonary and Critical Care Medicine, Center for Respiratory Diseases, China–Japan Friendship Hospital, National Clinical Research Center for Respiratory Diseases, Beijing, China

    Department of Respiratory Medicine, Capital Medical University, Beijing, China
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  • Author Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    Guangmei Zhang
    Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    Affiliations
    Yucheng People’s Hospital, Yucheng City, Shangdong, China
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  • Author Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    Lingyu Gao
    Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    Affiliations
    Regional Measles Reference Laboratory for the Western Pacific Region of the World Health Organization and State Key Laboratory for Molecular Virology and Genetic Engineering, National Institute for Viral Disease Control and Prevention, Chinese Centers for Disease Control and Prevention, Beijing, China
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  • Author Footnotes
    2 Wenbo Xu and Bin Cao contributed equally to this work.
    Wenbo Xu
    Correspondence
    Corresponding author at: National Institute for Viral Disease Control and Prevention, Chinese Centers for Disease Control and Prevention, Changbai Road 155th, 102206, Changping District, Beijing, China.
    Footnotes
    2 Wenbo Xu and Bin Cao contributed equally to this work.
    Affiliations
    Regional Measles Reference Laboratory for the Western Pacific Region of the World Health Organization and State Key Laboratory for Molecular Virology and Genetic Engineering, National Institute for Viral Disease Control and Prevention, Chinese Centers for Disease Control and Prevention, Beijing, China
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  • Author Footnotes
    2 Wenbo Xu and Bin Cao contributed equally to this work.
    Bin Cao
    Correspondence
    Corresponding author at: Department of Pulmonary and Critical Care Medicine, China–Japan Friendship Hospital, 2nd Yinghua East Street, 100029, Chaoyang District, Beijing, China.
    Footnotes
    2 Wenbo Xu and Bin Cao contributed equally to this work.
    Affiliations
    Beijing Chaoyang Hospital of Capital Medical University, Beijing, China

    Department of Pulmonary and Critical Care Medicine, Center for Respiratory Diseases, China–Japan Friendship Hospital, National Clinical Research Center for Respiratory Diseases, Beijing, China

    Department of Respiratory Medicine, Capital Medical University, Beijing, China
    Search for articles by this author
  • Author Footnotes
    1 Donghao Yu, Guangmei Zhang, and Lingyu Gao contributed equally to this work.
    2 Wenbo Xu and Bin Cao contributed equally to this work.
Open AccessPublished:August 28, 2018DOI:https://doi.org/10.1016/j.ijid.2018.08.015

      Highlights

      • Vaccinated individuals with measles present with nodular pneumonia.
      • Varying amounts of nodules were observed in the chest computed tomography scans of the cases.
      • A high ratio of measles-specific IgG/IgM was found to be associated with nodular pneumonia.

      Abstract

      Background

      Vaccinated individuals infected with measles can develop nodular pneumonia. These cases can be misdiagnosed due to the absence of specific IgM and typical symptoms. An effective diagnostic tool is needed.

      Methods

      During March 2016, adult inpatients in Yucheng People’s Hospital were enrolled prospectively and included in the study. Patients were included if samples were obtained ≤14 days from the onset of fever. Measles virus was detected by RT-PCR of the oropharyngeal swab sample. Chest computed tomography scans and medical records were obtained. Oropharyngeal swabs and blood samples were collected for IgM and IgG testing, RT-PCR, and gene sequencing.

      Results

      Sixteen patients were enrolled. Ten were found to have nodular pneumonia and were defined as the nodular group. The remaining six patients were defined as the control group. Measles-specific IgG titers in the nodular group were high (3618.3–5000 mIU/ml), while IgM titers were low (<25 mIU/ml); IgG titers in the control group were low (241.4–2560.3 mIU/ml), while IgM titers were high (137–5000 mIU/ml). No obvious viral mutation was detected in the nodular group.

      Conclusions

      Measles-associated nodular pneumonia was only evident in those patients with an IgG/IgM ratio >20. In measles outbreaks, the IgG/IgM ratio may be useful to identify nodular pneumonia.

      Keywords

      Introduction

      Measles is a highly contagious viral disease and was the cause of millions of deaths each year prior to the introduction of the measles vaccine. Since the introduction of the vaccine, the incidence of measles has dropped significantly (
      • Rota P.A.
      • Moss W.J.
      • Takeda M.
      • De Swart R.L.
      • Thompson K.M.
      • Goodson J.L.
      Measles.
      ). Immunity to measles was thought to be life-long (
      • Panum P.L.
      ), but it has been demonstrated that immunity wanes over time, regardless of whether immunity was acquired from a killed vaccine, live-attenuated vaccine, or natural infection (
      • Rauh L.W.
      • Schmidt R.
      Measles immunization with killed virus vaccine. Serum antibody titers and experience with exposure to measles epidemic.
      ,
      • Dai B.
      • Chen Z.H.
      • Liu Q.C.
      • Wu T.
      • Guo C.Y.
      • Wang X.Z.
      • et al.
      Duration of immunity following immunization with live measles vaccine: 15 years of observation in Zhejiang Province, China.
      ,
      • Kremer J.R.
      • Schneider F.
      • Muller C.P.
      Waning antibodies in measles and rubella vaccinees — a longitudinal study.
      ). Patients with reduced immunity may present with different symptoms, including atypical measles syndrome (Rauh and Schmidt, 1965) and modified measles (
      • Chen R.T.
      • Markowitz L.E.
      • Albrecht P.
      • Stewart J.A.
      • Mofenson L.M.
      • Preblud S.R.
      • et al.
      Measles antibody: reevaluation of protective titers.
      ).
      Atypical measles syndrome (AMS) is a specific type of measles illness, it occurs in individuals who were exposed to wild measles virus several years after they had the killed measles vaccine. These patients have a characteristic rash and particular type of pneumonia, and large, round consolidations are observed in the patient’s lungs (
      • Rauh L.W.
      • Schmidt R.
      Measles immunization with killed virus vaccine. Serum antibody titers and experience with exposure to measles epidemic.
      ,
      • Mitnick J.
      • Becker M.H.
      • Rothberg M.
      • Genieser N.B.
      Nodular residua of atypical measles pneumonia.
      ,
      • Yamamoto M.
      • Torii Y.
      • Kodama M.
      • Sugiura T.
      • Takada K.
      • Morishita M.
      • et al.
      [Atypical measles pneumonia in adolescents: pulmonary residual nodular lesion with cavity].
      ). Such cases have become rare since the killed measles vaccine was withdrawn.
      Modified measles was described by Chen in the 1990s. This illness may occur in individuals who have previously received the live-attenuated vaccination if they become infected with the measles virus (
      • Chen R.T.
      • Markowitz L.E.
      • Albrecht P.
      • Stewart J.A.
      • Mofenson L.M.
      • Preblud S.R.
      • et al.
      Measles antibody: reevaluation of protective titers.
      ,
      • Edmonson M.B.
      • Addiss D.G.
      • McPherson J.T.
      • Berg J.L.
      • Circo S.R.
      • Davis J.P.
      Mild measles and secondary vaccine failure during a sustained outbreak in a highly vaccinated population.
      ,
      • Hirose M.
      • Hidaka Y.
      • Miyazaki C.
      • Ueda K.
      • Yoshikawa H.
      Five cases of measles secondary vaccine failure with confirmed seroconversion after live measles vaccination.
      ,
      • Helfand R.F.
      • Kim D.K.
      • Gary H.E.
      • Edwards G.L.
      • Bisson G.P.
      • Papania M.J.
      • et al.
      Nonclassic measles infections in an immune population exposed to measles during a college bus trip.
      ,
      • Rota J.S.
      • Hickman C.J.
      • Sowers S.B.
      • Rota P.A.
      • Mercader S.
      • Bellini W.J.
      Two case studies of modified measles in vaccinated physicians exposed to primary measles cases: high risk of infection but low risk of transmission.
      ,
      • van den Hoek A.
      • Sonder G.J.
      • Scholing M.
      • Gijselaar D.B.
      • van Binnendijk R.S.
      Two cases of mild IgM-negative measles in previously vaccinated adults, the Netherlands, April and July 2011.
      ). Symptoms in these patients are usually mild and they may not present with the classical clinical symptoms, such as a rash and Koplik spots (
      • Chen R.T.
      • Markowitz L.E.
      • Albrecht P.
      • Stewart J.A.
      • Mofenson L.M.
      • Preblud S.R.
      • et al.
      Measles antibody: reevaluation of protective titers.
      ,
      • Helfand R.F.
      • Kim D.K.
      • Gary H.E.
      • Edwards G.L.
      • Bisson G.P.
      • Papania M.J.
      • et al.
      Nonclassic measles infections in an immune population exposed to measles during a college bus trip.
      ). Patients with modified measles are characterized by a rapid and robust response of measles-specific IgG, while IgM is fleeting or absent in serology (
      • Chen R.T.
      • Markowitz L.E.
      • Albrecht P.
      • Stewart J.A.
      • Mofenson L.M.
      • Preblud S.R.
      • et al.
      Measles antibody: reevaluation of protective titers.
      ,
      • Erdman D.D.
      • Heath J.L.
      • Watson J.C.
      • Markowitz L.E.
      • Bellini W.J.
      Immunoglobulin M antibody response to measles virus following primary and secondary vaccination and natural virus infection.
      ,
      • Hickman C.J.
      • Hyde T.B.
      • Sowers S.B.
      • Mercader S.
      • McGrew M.
      • Williams N.J.
      • et al.
      Laboratory characterization of measles virus infection in previously vaccinated and unvaccinated individuals.
      ). Serological test results of patients with modified measles are different from those of patients with a primary infection. Due to the absence of IgM and typical symptoms, modified measles cases may go undiagnosed.
      Nodular pneumonia has been reported in patients with modified measles (
      • Okano Y.
      • Motoki T.
      • Hatakeyama N.
      • Iwahara Y.
      • Nakamura Y.
      • Ogushi F.
      Atypical measles pneumonia presenting with multiple nodular opacities on chest radiographs.
      ,
      • Pang M.
      • Xu J.Y.
      • Li P.
      • Han X.X.
      • Li M.Y.
      [Clinical analysis of 51 cases of atypical measles syndrome characterized by fever and multiple lung lesions].
      ). Pneumonia and an absence of measles-specific IgM may lead to misdiagnosis and inappropriate antimicrobial treatment. An effective diagnostic tool for vaccinated individuals with measles-associated nodular pneumonia is needed.

      Methods

      During March 2016, inpatients in Yucheng People’s Hospital were enrolled prospectively. The inclusion criteria were (1) age 18 years and above; (2) diagnosed with measles according to the criteria of the Chinese Centers for Disease Control and Prevention (CDC), or diagnosed with nodular pneumonia; (3) the time from fever onset to sampling was ≤14 days. Patients were excluded if the measles virus was not detected by RT-PCR in their oropharyngeal swabs. This study was approved by the China–Japan Friendship Hospital Ethics Committee (reference number 2015-85).

      Case definition

      A confirmed case of measles was defined by the criteria of the CDC (

      Ministry of Health, the People's Republic of China. Diagnosis for measles. July 27, 2017. Available from: http://www.moh.gov.cn/zhuz/s9491/201707/c0f33d9c8f6e426f930a7f2c942dc637.shtml.

      ), i.e., patients must have one or more of the following symptoms: (1) fever, i.e., a temperature ≥38 °C; (2) onset of maculopapular rash from the face and the backs of the ears, generally extending to the whole body within 3–5 days; (3) upper respiratory symptoms such as cough, rhinorrhea, or sneezing, and eye symptoms such as photophobia, lachrymation, or conjunctivitis; (4) Koplik spots (can be observed within 2–3 days from illness onset), and any one of the following positive laboratory results: (1) an increase in measles-specific serum IgM in patients who have not been vaccinated in the last 8 days to 6 weeks; (2) isolation of the measles virus from nasopharyngeal or urine samples, or detection by RT-PCR; and (3) a four-fold increase in measles-specific IgG in convalescent serum, or a conversion from being IgG-negative in the acute phase to IgG-positive during the convalescent phase.

      Data collection

      Sixteen patients were enrolled in the study, and these included nine healthcare workers and seven patients admitted from the community. Once the participants had read and signed an informed consent agreement, the following information was obtained for each case: demographic characteristics, medical records, radiological images, vaccination history, history of recent contacts, and travel history. Data were documented in case reporting forms by a single researcher. Computed tomography (CT) scans were performed on all patients during the acute phase. Images were read by two respiratory physicians and a radiologist. All patients reported that they had been vaccinated as scheduled, but had not received any supplementary vaccination. China introduced the live-attenuated measles vaccine in 1965 and the inactivated vaccine has not been used.
      The data were analyzed using IBM SPSS Statistics version 22.0 (IBM Corp., Armonk, NY, USA). The symptoms of the two groups were compared using Fisher’s exact test. Routine blood and blood biochemical examinations were compared between the two groups using the Mann–Whitney U-test. Receiver operating characteristic curve analysis was used to determine the cut-off value for the IgG/IgM ratio.

      Samples collected

      Oropharyngeal swabs and blood samples were collected on March 8 and March 14, 2016. Double samples were collected by a single researcher and saved in virus preservation solution (3 ml per tube; the preservation solution consisted of 500 ml of minimum essential medium (MEM) maintenance fluid, 50 ml of 5% gelatin, 20 ml of 10 000 U/ml penicillin–streptomycin solution, 1 ml of 10 mg/ml gentamicin, and 200 μl of 0.25 mg/ml amphotericin). Blood samples were collected by a local hospital nurse. All samples were stored in an insulation box with ice maintained at 4 °C, which was transferred to the Chinese CDC within 24 h.

      Laboratory testing

      The quantitative results of measles-specific serum IgG and IgM were obtained using a commercial ELISA kit (Virion/Serion, Würzburg, Germany). Reverse transcription polymerase chain reaction (RT-PCR) and gene sequencing were performed in the measles laboratory of the Chinese CDC. Isolation of measles virus was performed using the Vero/hSLAM cell line, and the cells were harvested when <75% of the culture showed a cytopathic effect. RNA was extracted from oropharyngeal swabs using the QIAamp Viral RNA Mini Kit (Qiagen, Beijing, China), according to the manufacturer’s instructions (
      • Ono N.
      • Tatsuo H.
      • Hidaka Y.
      • Aoki T.
      • Minagawa H.
      • Yanagi Y.
      Measles viruses on throat swabs from measles patients use signaling lymphocytic activation molecule (CDw150) but not CD46 as a cellular receptor.
      ,
      • WHO
      New genotype of measles virus and update on global distribution of measles genotypes.
      ). RT-PCR was used to amplify the 550-nt coding for the COOH terminus of the N gene with the One Step PrimeScript RT-PCR Kit (TaKaRa, Dalian, China) and ProFlex ro Flexo Flexa. Sequences of the PCR products were derived by automated sequencing and BigDye terminator v3.0 chemistry according to the manufacturer’s protocol in both sense and antisense strands by an automated ABI PRISM 3100 DNA Sequencer (Perkin Elmer). Sequence proof reading and editing was conducted with Sequencer (Gene Codes Corporation). Sequence data were analyzed using BioEdit version 7.0 and phylogenetic analyses were performed using BioEdit and Mega 5.05. The robustness of the groupings was assessed using bootstrap resampling of 500 replicates and the trees were visualized with MEGA programs.

      Results

      The measles virus was detected in all 16 cases; they were thus all included in the analysis. Double samples were collected from all of the nine healthcare workers and one community patient. Single samples were collected in the acute period from the other six community patients, either because the acute phase was prior to their admission, or they had already been discharged.
      All 16 cases had no other underlying diseases. High-density nodules were randomly distributed in the chest CT scans of 10 patients, including a patient from the community, and these patients were defined as the nodular group: N1–N10, Figure 1. The diameter of the nodules was 1–2 cm, and some nodules could be found in the mediastinal window, but the nodules were difficult to observe in standard chest X-rays. Obvious changes were not observed in the lungs of the remaining six cases, and these patients were defined as the control group: C1–C6, Table 1. Healthcare worker N5 was revaluated with a CT scan after 2 months, and the nodules were absorbed well (Figure 2).
      Figure 1
      Figure 1A, B, C and D represent chest CT scans of four patients (N2, N4, N6, and N9, respectively) whose swabs were positive for the measles virus by reverse transcription polymerase chain reaction (RT-PCR). The arrows point to the nodules. High-density nodules were randomly distributed and the diameter of the nodules was 1–2 cm.
      Table 1Symptoms of the 16 cases.
      CaseSexAge, yearsSite of infectionOccupation in the hospitalDate of fever onset
      Some patients in the investigation did not have rash onset during the disease course; therefore, days from fever onset were calculated.
      FeverCoughCoryzaConjunctivitisRashKoplik spotSputumDyspneaSupplementary vaccinationOutcome
      C1F31CommunityNA27-FebYesYesYesYesYesYesYesNoNoRecovered
      C2M44CommunityNA25-FebYesYesNoYesYesYesYesNoNoRecovered
      C3M31CommunityNA26-FebYesYesNoYesYesYesYesNoNoRecovered
      C4F42CommunityNA23-FebYesYesYesYesYesYesYesNoNoRecovered
      C5M38CommunityNA6-MarYesYesNoYesYesYesYesNoNoRecovered
      C6F39CommunityNA7-MarYesYesNoYesYesYesYesNoNoRecovered
      N1M43HospitalEmergency physician2-MarYesYesNoNoNoNoNoNoNoRecovered
      N2M24HospitalTechnician in CT room27-FebYesNoNoNoNoNoNoNoNoRecovered
      N3F35HospitalTechnician in CT room27-FebYesNoNoNoNoNoNoNoNoRecovered
      N4M41HospitalTechnician in CT room27-FebYesYesNoNoNoNoNoNoNoRecovered
      N5M28HospitalTechnician in CT room25-FebYesNoNoNoNoNoNoNoNoRecovered
      N6F25HospitalEmergency clerk28-FebYesNoNoNoNoNoNoNoNoRecovered
      N7M36HospitalEngineer27-FebYesNoYesNoNoNoNoNoNoRecovered
      N8M36HospitalOrthopedist physician27-FebYesYesNoNoNoNoNoNoNoRecovered
      N9M43HospitalTechnician in B-ultrasound room25-FebYesNoYesYesYesYesNoNoNoRecovered
      N10M38CommunityNA6-MarYesYesNoYesYesYesNoNoNoRecovered
      p-Value
      The p-values for differences between the two groups were calculated with the Mann–Whitney U-test.
      0.4280.0260.4890.030.010.01<0.01
      CT, computed tomography; F, female; M, male; NA, not available.
      a Some patients in the investigation did not have rash onset during the disease course; therefore, days from fever onset were calculated.
      b The p-values for differences between the two groups were calculated with the Mann–Whitney U-test.
      Figure 2
      Figure 2A and B represent the chest CT of one case (N5) whose swab was positive for the measles virus by reverse transcription polymerase chain reaction (RT-PCR. B shows the same level of A after two months. Most of the nodules were absorbed, with only one still remaining to some extent..
      There was no difference between the two groups with respect to the time from onset to sampling (p = 0.868). Measles-specific IgG was high in the acute phase in the nodular group (more than 3600 mIU/ml), and it was still high in the second specimens of N1–N9 (more than 5000 mIU/ml), while an obvious IgG rise (more than 1000 mIU/ml) in the acute period was observed in only two patients in the control group. To calculate the ratio of IgG/IgM, IgG values greater than 5000 mIU/ml and IgM values of less than 25 mIU/ml were considered as 5000 mIU/ml and 25 mIU/ml, respectively. The cut-off value of the ratio of IgG/IgM in the acute period was 20.205. For ease of use, a cut-off ratio of 20 was deemed acceptable. In this investigation, patients with a ratio of IgG/IgM >20 had nodules, while those with a ratio <20 had no obvious changes in the lungs (Table 2).
      Table 2Measles-specific IgM and IgG concentrations in the 16 cases.
      CaseRashSample days after fever onset
      Some patients in the investigation did not have rash onset during the disease course; therefore, days from fever onset were calculated.
      RT-PCRGenotypeImmunoglobulin concentration (mIU/ml)Ratio of IgG/IgM
      As the limit for detecting IgM and IgG was 25–5000mIU/ml, the ratio was calculated from the upper limit of IgG and the lower limit of IgM.
      Number of nodules
      IgMIgG
      C1YesS110+NA192.32560.313.31NA
      C2YesS112+NA555.3640.21.15NA
      S218+1371612.711.77
      C3YesS111+NA1184241.40.20NA
      C4YesS114+NA241.18083.35NA
      C5YesS17+NA916.21538.51.68NA
      C6YesS18+NA>5000452<0.10NA
      N1NoS16+H1a<253618.3>144.735
      S212<25>5000>200
      N2NoS110+H1a<25>5000>2004
      S216<25>5000>200
      N3NoS110+H1a<25>5000>2007
      S216<25>5000>200
      N4YesS110+H1a<25>5000>2002
      S216<25>5000>200
      N5NoS112+H1a<25>5000>2008
      S218<25>5000>200
      N6NoS19+H1a<25>5000>2002
      S21568.2>5000>73.31
      N7NoS110+NA<25>5000>2004
      S216<25>5000>200
      N8NoS110+NA<25>5000>20017
      S216<25>5000>200
      N9YesS112+H1a<25>5000>2003
      S218<25>5000>200
      N10YesS18+NA181.3491427.105
      S1, the first sample; S2, the second sample; NA, not available.
      a Some patients in the investigation did not have rash onset during the disease course; therefore, days from fever onset were calculated.
      b As the limit for detecting IgM and IgG was 25–5000 mIU/ml, the ratio was calculated from the upper limit of IgG and the lower limit of IgM.
      Genetic sequencing was performed for seven patients in the nodular group (Figure 3). The nucleotide sequence data of the virus from the seven samples were deposited in GenBank under accession numbers MH483529–MH483535. The measles virus was subtyped as H1a, the most common measles virus in China (
      • Zhang Y.
      • Ji Y.-X.
      • Zhu Z.
      [Circulating pattern analysis for endemic measles viruses in mainland of China].
      ,
      • Zhang Y.
      • Xu S.
      • Wang H.
      • Zhu Z.
      • Ji Y.
      • Liu C.
      • et al.
      Single endemic genotype of measles virus continuously circulating in China for at least 16 years.
      ). On comparison with 11 measles virus strains collected from different cities in Shandong Province in March 2016, no obvious mutation was found.
      Figure 3
      Figure 3A phylogenetic tree of samples from patients with nodular pneumonia (black circles), measles wild-type virus strains of Shandong China in Mar 2016 (red squares) and WHO reference MeV strains, based on the 456 nucleotide sequences coding for the COOH-terminus of the nucleoprotein. The virus in the outbreak belongs to subtype H1a, which is the predominant virus circulating in Shandong.
      All 16 patients recovered without complications.

      Discussion

      In this study, measles-associated nodular pneumonia did not appear to be caused by a mutated virus but rather via an immune response. The serological results of the 16 patients with measles suggested that a ratio of measles-specific IgG/IgM >20 was associated with the appearance of nodular pneumonia.
      A high ratio of IgG/IgM may be the result of a more intense response to the virus. When waning immunity can no longer fully protect vaccinated individuals from the measles virus, a rapid and robust IgG response to an infection is typical, compared with an initially slow response in unvaccinated individuals (
      • Hickman C.J.
      • Hyde T.B.
      • Sowers S.B.
      • Mercader S.
      • McGrew M.
      • Williams N.J.
      • et al.
      Laboratory characterization of measles virus infection in previously vaccinated and unvaccinated individuals.
      ,
      • Rota J.S.
      • Hickman C.J.
      • Sowers S.B.
      • Rota P.A.
      • Mercader S.
      • Bellini W.J.
      Two case studies of modified measles in vaccinated physicians exposed to primary measles cases: high risk of infection but low risk of transmission.
      ). On the other hand, IgM may be negative or fleeting in vaccinated patients with a measles infection (
      • Hickman C.J.
      • Hyde T.B.
      • Sowers S.B.
      • Mercader S.
      • McGrew M.
      • Williams N.J.
      • et al.
      Laboratory characterization of measles virus infection in previously vaccinated and unvaccinated individuals.
      ). Nodular pneumonia may be a result of this type of immune response. The measles virus can infect individuals with waning immunity and can replicate in local lymphoid tissue, then spread through the blood stream (
      • Rota P.A.
      • Moss W.J.
      • Takeda M.
      • De Swart R.L.
      • Thompson K.M.
      • Goodson J.L.
      Measles.
      ,
      • Moss W.J.
      Measles.
      ). Nodules may be caused by type III hypersensitivity. During the process of dissemination, IgG is produced and it binds to the measles virus to form an antigen–antibody complex. As the measles virus is disseminated to many organs via viremia, nodules caused by these immune complexes can be seen in these organs (
      • Melenotte C.
      • Cassir N.
      • Tessonnier L.
      • Brouqui P.
      Atypical measles syndrome in adults: still around.
      ). However such a response may also limit the replication of the virus, and may explain why most patients with nodular pneumonia have no rash, fewer respiratory symptoms, are less contagious, and have less liver and myocardial injury. Compared with atypical measles symptoms, infiltrates in the lungs of patients with modified measles are less, and peripheral blood eosinophilia (
      • Polack F.P.
      • Auwaerter P.G.
      • Lee S.H.
      • Nousari H.C.
      • Valsamakis A.
      • Leiferman K.M.
      • et al.
      Production of atypical measles in rhesus macaques: evidence for disease mediated by immune complex formation and eosinophils in the presence of fusion-inhibiting antibody.
      ) was not observed in this study. The mechanism of the nodular pneumonia observed in the cases of modified measles in the present study may be different from that observed in atypical measles.
      Nodular pneumonia in individuals vaccinated for measles may appear in the acute period and the nodules are absorbed slowly. In this investigation, nodules were found as early as the second day after the onset of fever, and some nodules were still present in the chest scans of one case 2 months later (even though the RT-PCR was negative in the second oropharyngeal swab of this patient). In a previous report of 51 cases with modified measles, 48 cases were observed to have nodular pneumonia, and a few nodules were still found in four patients at follow-up about 2 months after discharge from the hospital (
      • Pang M.
      • Xu J.Y.
      • Li P.
      • Han X.X.
      • Li M.Y.
      [Clinical analysis of 51 cases of atypical measles syndrome characterized by fever and multiple lung lesions].
      ). Another case report described nodules in the lungs of a female patient with modified measles, and some of the nodules were still present in the CT scans 8 months later (
      • Okano Y.
      • Motoki T.
      • Hatakeyama N.
      • Iwahara Y.
      • Nakamura Y.
      • Ogushi F.
      Atypical measles pneumonia presenting with multiple nodular opacities on chest radiographs.
      ).
      In this study, most of the infected healthcare workers worked in the CT room, which has no window and is frequented by numerous patients. Measles infectious droplets have been reported to remain in the air for more than 2 h (
      • Hope K.
      • Boyd R.
      • Conaty S.
      • Maywood P.
      Measles transmission in health care waiting rooms: implications for public health response.
      ), and it is assumed that the outbreak was caused by a patient with measles who had not yet had the rash onset. The virus could have been spread in the emergency department and CT room, and physicians in other departments would have had a chance of becoming infected when they stepped into the room. Measles outbreaks can occur easily in crowded settings such as hospitals (
      • Zhang Z.
      • Zhao Y.
      • Yang L.
      • Lu C.
      • Meng Y.
      • Guan X.
      • et al.
      Measles outbreak among previously immunized adult healthcare workers, China, 2015.
      ). Hospitals should be aware that insufficiently ventilated rooms such as these are a risk for infectious disease outbreaks.
      This study also highlights the necessity of supplementary immunization activity (SIA). All of the 16 patients in this study had been vaccinated once but had not received supplementary immunization. Patients such as these may facilitate the transmission of the measles virus in the population. Although patients who have been vaccinated are thought not to shed the measles virus (
      • Lievano F.A.
      • Papania M.J.
      • Helfand R.F.
      • Harpaz R.
      • Walls L.
      • Katz R.S.
      • et al.
      Lack of evidence of measles virus shedding in people with inapparent measles virus infections.
      ,
      • Rota J.S.
      • Hickman C.J.
      • Sowers S.B.
      • Rota P.A.
      • Mercader S.
      • Bellini W.J.
      Two case studies of modified measles in vaccinated physicians exposed to primary measles cases: high risk of infection but low risk of transmission.
      ), contagious cases have been reported (
      • Rosen J.B.
      • Rota J.S.
      • Hickman C.J.
      • Sowers S.B.
      • Mercader S.
      • Rota P.A.
      • et al.
      Outbreak of measles among persons with prior evidence of immunity, New York City, 2011.
      ,
      • Ma R.
      • Lu L.
      • Zhangzhu J.
      • Chen M.
      • Yu X.
      • Wang F.
      • et al.
      A measles outbreak in a middle school with high vaccination coverage and evidence of prior immunity among cases, Beijing, P.R. China.
      ). Supplementary immunization activity can increase the protection of individuals with waned immunity and close immunity gaps. The recent resurgence of measles in some countries with high vaccination coverage highlights the importance of SIA. Migrants, refugees, and international travelers may import diseases, and outbreaks may occur (
      • Chen T.-H.
      • Kutty P.
      • Lowe L.E.
      • Hunt E.A.
      • Blostein J.
      • Espinoza R.
      • et al.
      Measles outbreak associated with an international youth sporting event in the United States, 2007.
      ,
      • Nakken C.S.
      • Skovdal M.
      • Nellums L.B.
      • Friedland J.S.
      Vaccination status and needs of asylum-seeking children in Denmark: a retrospective data analysis.
      ). There is a need to develop strategies to facilitate and monitor such individuals at high risk of developing infectious diseases, and provide access to vaccinations (
      • Kinsman J.
      • Stöven S.
      • Elgh F.
      • Murillo P.
      • Sulzner M.
      Good practices and challenges in addressing poliomyelitis and measles in the European Union.
      ,

      Giambi C, Del M, Dalla T, Riccardo F, Bella A, Grazia M, et al. National immunization strategies targeting migrants in six European countries. 2018 [Epub ahead of print]. Available from: http://www.ncbi.nlm.nih.gov/pubmed/29426661.

      ).
      There are some limitations to this study. Firstly, IgG titers above 5000 mIU/ml could not be obtained due to the limited capability of the equipment. Secondly, a biopsy of the nodules was not done as the patient’s refused this procedure due to their mild symptoms. Thirdly, the number of cases was limited and data from more patients should be collected to confirm the conclusions presented here. Finally, all measles viruses sequenced were H1a, and it was not possible to confirm that this type of pneumonia is specific to the H1a genotype. The viral samples in the control group were not sequenced, as more than 99% of measles virus isolated in Shandong Province is H1a. This may be a limitation in the interpretation of the measles genotype with nodular pneumonia.
      In the measles season, measles virus should be considered as a potential pathogen in cases of patients with nodular pneumonia. The ratio of measles-specific IgG/IgM may be a useful tool to identify these patients, as we found nodular pneumonia to be evident only in those patients with an IgG/IgM ratio >20.

      Funding

      This study was supported by a National Science Grant for Distinguished Young Scholars (grant numbers 81425001/H0104), a National Key Technology Support Program from the Ministry of Science and Technology (grant numbers 2015BAI12B11), and the Beijing Science and Technology Project (grant numbers D151100002115004).

      Ethical approval

      This study was approved by the China–Japan Friendship Hospital Ethics Committee (reference number 2015-85).

      Conflict of interest

      All authors report no conflict of interest.

      Appendix A. Supplementary data

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