Ashleigh R. Tuite, PhD, MPH; Isaac I. Bogoch, MD; Ryan Sherbo, MSc; Alexander Watts, PhD; David Fisman, MD, MPH; Kamran Khan, MD, MPH
Note: Drs. Tuite and Bogoch contributed equally to this work.
Grant Support: By grant 02179-000 from the Canadian Institutes of Health Research.
Disclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M20-0696.
Reproducible Research Statement: Study protocol: Not applicable. Statistical code: Available from Dr. Tuite (firstname.lastname@example.org). Data set: Available from Dr. Khan (email@example.com).
Previous Posting: This manuscript was posted as a preprint on medRxiv on 25 February 2020. doi:10.1101/2020.02.24.20027375
Top 20 international cities connected to Iran by commercial air travel and associated vulnerability to infectious disease outbreaks.
Vulnerability is measured at the country level by using the IDVI score, with a lower value indicating reduced capacity to respond to outbreaks. Countries with the lowest IDVI scores are indicated in green. The top 20 cities accounted for 70% of international outbound traveler volumes from Iran in February 2019. The first and 20th ranked cities, Istanbul and Milan, had 46 550 and 2500 outbound passengers, respectively, during this period. IDVI = Infectious Disease Vulnerability Index.
Estimated outbreak size in Iran required to observe exported cases internationally.
The estimated cumulative number of COVID-19 cases in Iran required to observe 3 cases exported to UAE, LBN, and CAN is shown in green. We also estimated the outbreak size required under alternate scenarios, including no additional exported cases to any other international destinations despite perfect case detection and 1 additional exported case to IRQ, AZE, or SYR (independently or to all 3 countries). Mean and 95% CIs are presented. The rate at which persons become infected while in Iran was assumed to be the same for residents and visitors. The rate of infection among air passengers (λ) was estimated as number of exported cases ÷ person-time at risk while in Iran. Person-time at risk was calculated as number of outbound air passengers × (average length of stay for visitors × proportion of air passengers who are visitors + outbreak duration × proportion of air passengers who are residents of Iran).
Outbreak size in Iran was then estimated as λ × population size of Iran × outbreak duration. AZE = Azerbaijan; CAN = Canada; COVID-19 = coronavirus disease 2019; IRQ = Iraq; LBN = Lebanon; SYR = Syria; UAE = United Arab Emirates.
Hamid Sharifi1, Mohammad Karamouzian1, Zahra Khorrami1, Malahat Khalili1, Ehsan Mostafavi2, Sana Eybpoush2, Ali Mirzazadeh3,1, Ali Akbar Haghdoost4*
1- HIV/STI Surveillance Research Center, and WHO Collaborating Center for HIV Surveillance, Institute for Futures Studies in Health, Kerman University of Medical Sciences, Kerman, Iran 2- Department o
March 20, 2020
Conflict of Interest:
Ali Akbar Haghdoost is the Deputy Minister of Health in Iran. The rest of the authors have no conflict of interest to disclose.
The accuracy of modeling the burden of COVID-19 in Iran with international airline travelers’ data
We read a recent modelling study by Tuite et al. published in Annals of Internal Medicine (1) with interest. The authors estimated the number of COVID-19 cases in Iran at 18,300 (95% CI: 3,770-53,470) cases until February 23rd, 2020 in a worst-case scenario and 1,820 (95% CI: 380-5,320 cases) cases in a best-case scenario. As people who are actively engaged in addressing the COVID-19 pandemic in Iran, we are concerned about the accuracy of these estimates.
First, the Infectious Disease Vulnerability Index (IDVI) was developed as a tool to provide international agencies with a better understanding of countries’ vulnerability to infectious disease outbreaks in a rather ‘normal’ situation and therefore, would underestimate their capacities during the outbreaks —including the COVID-19— where surveillance systems are much more sensitive and case detection is enhanced. Underestimating the IDVI during outbreaks might have indeed led to an overestimation of the COVID-19 burden in Iran.
Second, the estimated number of people infected with COVID-19 is highly dependent on the onset date of the epidemic. The authors assumed that the COVID-19 epidemic in Iran initiated in early January 2020 without providing sufficient support to back this assumption; a decision that could have significantly overestimated the number of infected cases in the last week of February when this modeling was done. At that time, Iran was not even among the top 50 international destinations from different cities in China, and therefore it is unlikely that the epidemic in Iran started in early January in Iran (2).
Third, the estimates assumed similar prevalence of COVID-19 in cities with and without international airports which would introduce bias into the modeling process. The chance of exposure to COVID-19 through national/international travels is heterogonous across cities with and without national/international airports, with the latter being much less exposed to the virus via this route (3). Around 30% of the Iran’s population live in rural area and out of 54 airports in Iran, only 13 are international airports which are located in 12 out of 434 cities (4). Assuming the same prevalence of the infection for the whole population may indeed overestimate the overall prevalence of COVID-19 in Iran.
Lastly, the prevalence estimates are based on data from United Nations World Tourism Organization (UNWTO) for the proportion of international travelers that are residents of Iran and the average length of stay of tourists in Iran. Therefore, the number of days that people infected with COVID-19 were actually inside Iran is unclear. Given the incubation period of COVID-19 ranging from 2-14 days, with possible outliers of 0-27 days (5), it is unclear whether the travelers identified in other countries with Iranian origin, got the infection in Iran or they were already infected prior to their last stay in the country.
In brief, there are major uncertainties about the COVID-19 epidemic and burden in Iran. By March 17, 2020, Iran’s surveillance system has detected 16,169 confirmed cases and 988 deaths with COVID-19 that have been reported in 31 provinces. The true magnitude of the epidemic, however, may take some time to be known. Simultaneous surveillance studies and epidemiologic field investigations are urgently needed to better estimate the extent of the epidemic in Iran and elsewhere. While such mathematical modeling of COVID-19 might be helpful in tackling the epidemic, they may be misleading if not viewed with a critical eye for their limitations and subjective assumptions.
1. Tuite AR, Bogoch II, Sherbo R, et al. Estimation of Coronavirus Disease 2019 (COVID-19) Burden and Potential for International Dissemination of Infection From Iran. Ann Intern Med. 2020; [Epub ahead of print 16 March 2020]. doi: https://doi.org/10.7326/M20-0696
2. International Air Transport Association. Annual Review 2019. Accessed at https://www.iata.org/contentassets/c81222d96c9a4e0bb4ff6ced0126f0bb/iata-annual-review-2019.pdf on 13 March 2020.
3. Fraser C, Donnelly CA, Cauchemez S, et al. WHO Rapid Pandemic Assessment Collaboration. Pandemic potential of a strain of inﬂuenzaA (H1N1): early ﬁndings. Science. 2009; 324:1557-61. [PMID: 19433588] doi:10.1126/science .1176062
4. Ministry of Roads and Urban Development, Iran Airports and Air Navigation Company. Accessed at https://statistics.airport.ir/.17 march 2020.
5. Guan, Wei-jie, et al. "Clinical characteristics of coronavirus disease 2019 in China." N Engl J Med (2020). doi: 10.1056/NEJMoa2002032
University of Toronto
March 23, 2020
Response to Sharifi et al.
Thank you for this thoughtful comment on our article. I am pleased to respond on behalf of my coauthors. Forensic estimation of epidemic size has many challenges, many of which are enumerated in this thoughtful letter. However, our estimates appear to have been substantially validated by a number of other external observations (1) not least of which relates to identification of new, large, burial sites in Iran visible on satellite imagery since the epidemic began there (2). We are pleased to see that a robust disease control effort, which includes more extensive testing, is now underway in Iran. We wish our Iranian colleagues success in this endeavour.References1. Wood G. Iran Has Far More Coronavirus Cases Than It Is Letting On. Available via the Internet at https://www.theatlantic.com/ideas/archive/2020/03/irans-coronavirus-problem-lot-worse-it-seems/607663/. Last accessed March 23, 2020. The Atlantic. 2020.2. Kottasova I, Murphy P. Satellite images show Iran building burial pits for coronavirus victims. CNN Online Available via the Internet at https://wwwcnncom/2020/03/13/middleeast/iran-coronavirus-mass-graves-intl/indexhtml Last accessed March 23, 2020. 2020.
Tuite AR, Bogoch II, Sherbo R, et al. Estimation of Coronavirus Disease 2019 (COVID-19) Burden and Potential for International Dissemination of Infection From Iran. Ann Intern Med. 2020;:. [Epub ahead of print 16 March 2020]. doi: https://doi.org/10.7326/M20-0696
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