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Preliminary estimation of the novel coronavirus disease (COVID-19) cases in Iran: A modelling analysis based on overseas cases and air travel data

Open AccessPublished:March 11, 2020DOI:https://doi.org/10.1016/j.ijid.2020.03.019

      Highlights

      • As of March 1, 2020, Iran had reported 987 COVID-19 cases, including 54 associated deaths.
      • At least six neighboring countries (Bahrain, Iraq, Kuwait, Oman, Afghanistan, and Pakistan) had reported imported COVID-19 cases from Iran.
      • We estimated that 16 533 (95% confidence interval 5925–35 538) COVID-19 cases had occurred in Iran by February 25, 2020.
      • Iran’s ascertainment rate could have been at a level of 0.6% on February 25, 2020.

      Abstract

      As of March 1, 2020, Iran had reported 987 novel coronavirus disease (COVID-19) cases, including 54 associated deaths. At least six neighboring countries (Bahrain, Iraq, Kuwait, Oman, Afghanistan, and Pakistan) had reported imported COVID-19 cases from Iran. In this study, air travel data and the numbers of cases from Iran imported into other Middle Eastern countries were used to estimate the number of COVID-19 cases in Iran. It was estimated that the total number of cases in Iran was 16 533 (95% confidence interval: 5925–35 538) by February 25, 2020, before the UAE and other Gulf Cooperation Council countries suspended inbound and outbound flights from Iran.

      Keywords

      Introduction

      The coronavirus disease 2019 (COVID-19) was first reported in Wuhan, Hubei Province, China at the end of 2019, and soon spread to the rest of China and overseas (
      • Bogoch I.I.
      • Watts A.
      • Thomas-Bachli A.
      • Huber C.
      • Kraemer M.U.
      • Khan K.
      Potential for global spread of a novel coronavirus from China.
      ). At the time of writing, 78 630 cases had been reported in China and 3664 cases had been confirmed in 46 other countries (
      • World Health Organization
      Coronavirus disease 2019 (COVID-19) situation report — 36.
      ). Iran has recently become an epicenter in the Middle East region and has seen the largest cumulative number of deaths outside China (). As of March 1, 2020, Iran had confirmed 987 COVID-19 cases, including 54 associated deaths (). At least six neighboring countries (Bahrain, Iraq, Kuwait, Oman, Afghanistan, and Pakistan) had reported imported COVID-19 cases from Iran. Given the serious concerns over the under-ascertainment of COVID-19 cases in Iran (), the United Arab Emirates (UAE) along with other Gulf Cooperation Council countries suspended inbound and outbound flights from Iran on February 25, 2020 ().
      In this study, air travel data and the numbers of cases from Iran imported into other Middle Eastern countries were used to estimate the number of COVID-19 cases in Iran. The calculated estimates were then compared to the number of reported cases in Iran to determine the extent of under-ascertainment.

      Materials and methods

      Data

      We obtained data on the transport capability of international airlines from 30 major airports in Iran covering the period February 1 to February 24, 2020 (
      • WorldData
      The 30 largest airports and airlines in Iran.
      ), from the VariFlight platform (https://data.variflight.com/). The numbers of exported cases from Iran to other countries in the Middle East were collected (
      • World Health Organization
      Coronavirus disease 2019 (COVID-19) situation report — 36.
      ). The population size of Iran was obtained from the World Bank (https://data.worldbank.org/), and was 81 800 269 in 2018. Table 1 shows the daily passenger numbers from Iran and the total reported cases in Middle Eastern countries used in our calculations.
      Table 1Daily passenger numbers and the total numbers of reported cases in the Middle Eastern countries used in the estimation as of February 25, 2020.
      CountryDaily passengers from IranReported cases from Iran
      United Arab Emirates18332
      Lebanon1401
      Oman5002

      Methods

      In accordance with the study by Imai et al. (
      • Imai N.
      • Dorigatti I.
      • Cori A.
      • Riley S.
      • Ferguson N.M.
      Estimating the potential total number of novel coronavirus (2019-nCoV) cases in Wuhan City, China.
      ), it was assumed that the number of cases (n) exported from Iran followed a binomial distribution with size N and probability p. Here, N represents the total number of cases infected in Iran, and p is the probability that one case is detected outside the country. We approximated p as the ratio of daily outbound passengers from Iran (D) over the total size of the population (M) that those airports serve and multiplying it by the mean duration (t) from exposure to detection; thus, p = D∙t/M. We set t at 10 days, based on the study by Imai et al. (
      • Imai N.
      • Dorigatti I.
      • Cori A.
      • Riley S.
      • Ferguson N.M.
      Estimating the potential total number of novel coronavirus (2019-nCoV) cases in Wuhan City, China.
      ). It was assumed that the catchment population was the total population of Iran. The maximum likelihood estimate of the total number of COVID-19 cases in Iran (λ) was calculated by fitting the model to the number of confirmed cases with a binomial-distributed likelihood framework. As shown in Equation (1), the l() represents the total log-likelihood and k is the total number of countries we selected. The 95% confidence intervals (CI) were calculated using the profile likelihood estimation approach determined by a Chi-square quantile.
      l(λ)=logLλ=i=1klogfni,pi;λ
      (1)


      To explore alternative scenarios, a smaller catchment population (60 000 000) and a shorter detection window (8 days) were also considered. We considered a baseline scenario with a 100% attendance rate for each aircraft. In addition, we tested the situations of 90% and 70% flight attendance rates and keeping the other conditions same as the baseline scenario.

      Results and discussion

      The total number of cases in Iran was estimated to be 16 533 (95% CI 5925–35 538) by February 25, 2020. Table 2 summarizes the sensitivity analysis of varying the baseline assumptions and the alternative scenarios for the catchment population, detection window, and attendance rates.
      Table 2Estimated case numbers based on the baseline assumptions and alternative scenarios.
      Effective catchment populationDetection window (day)Total cases (95% CI)
      Baseline81 800 2691016 533 (5925–35 538)
      Smaller catchment60 000 0001012 125 (4345–12 145)
      Shorter detection window81 800 269820 667 (7408–44 424)
      90% load factor81 800 2691018 368 (6583–39 482)
      70% load factor81 800 2691023 627 (8472–50 780)
      CI, confidence interval.
      As suggested by Zhao et al. (
      • Zhao S.
      • Musa S.S.
      • Lin Q.
      • Ran J.
      • Yang G.
      • Wang W.
      • et al.
      Estimating the unreported number of novel coronavirus (2019-nCoV) cases in China in the first half of january 2020: a data-driven modelling analysis of the early outbreak.
      ), underreporting likely occurred during the early stage of the COVID-19 outbreak, due to the shortage of diagnostic kits and inadequate screening of suspected cases (
      • Imai N.
      • Dorigatti I.
      • Cori A.
      • Riley S.
      • Ferguson N.M.
      Estimating the potential total number of novel coronavirus (2019-nCoV) cases in Wuhan City, China.
      ). A recent study by Tuite et al. (
      • Tuite A.R.
      • Bogoch I.
      • Sherbo R.
      • Watts A.
      • Fisman D.N.
      • Khan K.
      Estimation of COVID-2019 burden and potential for international dissemination of infection from Iran.
      ) estimated a total of 18 300 (95% CI 3770–53 470) cases in Iran by February 25, 2020. Our estimates are consistent with those of Tuite et al. (
      • Tuite A.R.
      • Bogoch I.
      • Sherbo R.
      • Watts A.
      • Fisman D.N.
      • Khan K.
      Estimation of COVID-2019 burden and potential for international dissemination of infection from Iran.
      ), although we used a slightly different approach and a flight data source. We now have two studies with almost identical results.
      In conclusion, Iran’s ascertainment rate could have been at a level of 0.6% on February 25, 2020. The health security capabilities of many countries in the Middle East are below the world average (
      • GHS Index
      2019 global health security index.
      ), which means that if the epidemic in Iran continues to spread to neighboring countries, the fragile public health systems of Middle Eastern countries are likely to experience difficulty coping with the outbreak.

      Funding

      DH was supported by a General Research Fund (15205119) from the Research Grants Council of Hong Kong and an Alibaba (China)–Hong Kong Polytechnic University Collaborative Research Project.

      Ethical approval and consent to participate

      Not applicable.

      Availability of data and materials

      All data and materials used in this work are publicly available.

      Consent for publication

      Not applicable.

      Conflict of interest

      DH was supported by an Alibaba (China)–Hong Kong Polytechnic University Collaborative Research Project. All other authors declared no competing interests.

      Disclaimer

      The funding agencies had no role in the design and conduct of the study, the collection, management, analysis, and interpretation of the data, the preparation, review, and approval of the manuscript, or in the decision to submit the manuscript for publication.

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