BACKGROUND: Asymptomatic or subclinical SARS-CoV-2 infections are often unreported, which means that confirmed case counts may not accurately reflect underlying epidemic dynamics. Understanding the level of ascertainment (the ratio of confirmed symptomatic cases to the true number of symptomatic individuals) and undetected epidemic progression is crucial to informing COVID-19 response planning, including the introduction and relaxation of control measures. Estimating case ascertainment over time allows for accurate estimates of specific outcomes such as seroprevalence, which is essential for planning control measures. METHODS: Using reported data on COVID-19 cases and fatalities globally, we estimated the proportion of symptomatic cases (i.e. any person with any of fever ≥ 37.5 °C, cough, shortness of breath, sudden onset of anosmia, ageusia or dysgeusia illness) that were reported in 210 countries and territories, given those countries had experienced more than ten deaths. We used published estimates of the baseline case fatality ratio (CFR), which was adjusted for delays and under-ascertainment, then calculated the ratio of this baseline CFR to an estimated local delay-adjusted CFR to estimate the level of under-ascertainment in a particular location. We then fit a Bayesian Gaussian process model to estimate the temporal pattern of under-ascertainment. RESULTS: Based on reported cases and deaths, we estimated that, during March 2020, the median percentage of symptomatic cases detected across the 84 countries which experienced more than ten deaths ranged from 2.4% (Bangladesh) to 100% (Chile). Across the ten countries with the highest number of total confirmed cases as of 6 July 2020, we estimated that the peak number of symptomatic cases ranged from 1.4 times (Chile) to 18 times (France) larger than reported. Comparing our model with national and regional seroprevalence data where available, we find that our estimates are consistent with observed values. Finally, we estimated seroprevalence for each country. As of 7 June, our seroprevalence estimates range from 0% (many countries) to 13% (95% CrI 5.6-24%) (Belgium). CONCLUSIONS: We found substantial under-ascertainment of symptomatic cases, particularly at the peak of the first wave of the SARS-CoV-2 pandemic, in many countries. Reported case counts will therefore likely underestimate the rate of outbreak growth initially and underestimate the decline in the later stages of an epidemic. Although there was considerable under-reporting in many locations, our estimates were consistent with emerging serological data, suggesting that the proportion of each country's population infected with SARS-CoV-2 worldwide is generally low.
BACKGROUND: Asymptomatic or subclinical SARS-CoV-2 infections are often unreported, which means that confirmed case counts may not accurately reflect underlying epidemic dynamics. Understanding the level of ascertainment (the ratio of confirmed symptomatic cases to the true number of symptomatic individuals) and undetected epidemic progression is crucial to informing COVID-19 response planning, including the introduction and relaxation of control measures. Estimating case ascertainment over time allows for accurate estimates of specific outcomes such as seroprevalence, which is essential for planning control measures. METHODS: Using reported data on COVID-19 cases and fatalities globally, we estimated the proportion of symptomatic cases (i.e. any person with any of fever ≥ 37.5 °C, cough, shortness of breath, sudden onset of anosmia, ageusia or dysgeusia illness) that were reported in 210 countries and territories, given those countries had experienced more than ten deaths. We used published estimates of the baseline case fatality ratio (CFR), which was adjusted for delays and under-ascertainment, then calculated the ratio of this baseline CFR to an estimated local delay-adjusted CFR to estimate the level of under-ascertainment in a particular location. We then fit a Bayesian Gaussian process model to estimate the temporal pattern of under-ascertainment. RESULTS: Based on reported cases and deaths, we estimated that, during March 2020, the median percentage of symptomatic cases detected across the 84 countries which experienced more than ten deaths ranged from 2.4% (Bangladesh) to 100% (Chile). Across the ten countries with the highest number of total confirmed cases as of 6 July 2020, we estimated that the peak number of symptomatic cases ranged from 1.4 times (Chile) to 18 times (France) larger than reported. Comparing our model with national and regional seroprevalence data where available, we find that our estimates are consistent with observed values. Finally, we estimated seroprevalence for each country. As of 7 June, our seroprevalence estimates range from 0% (many countries) to 13% (95% CrI 5.6-24%) (Belgium). CONCLUSIONS: We found substantial under-ascertainment of symptomatic cases, particularly at the peak of the first wave of the SARS-CoV-2 pandemic, in many countries. Reported case counts will therefore likely underestimate the rate of outbreak growth initially and underestimate the decline in the later stages of an epidemic. Although there was considerable under-reporting in many locations, our estimates were consistent with emerging serological data, suggesting that the proportion of each country's population infected with SARS-CoV-2 worldwide is generally low.
Authors: Seth Flaxman; Swapnil Mishra; Axel Gandy; H Juliette T Unwin; Thomas A Mellan; Helen Coupland; Charles Whittaker; Harrison Zhu; Tresnia Berah; Jeffrey W Eaton; Mélodie Monod; Azra C Ghani; Christl A Donnelly; Steven Riley; Michaela A C Vollmer; Neil M Ferguson; Lucy C Okell; Samir Bhatt Journal: Nature Date: 2020-06-08 Impact factor: 49.962
Authors: Jon C Emery; Timothy W Russell; Yang Liu; Joel Hellewell; Carl Ab Pearson; Gwenan M Knight; Rosalind M Eggo; Adam J Kucharski; Sebastian Funk; Stefan Flasche; Rein Mgj Houben Journal: Elife Date: 2020-08-24 Impact factor: 8.140
Authors: Silvia Stringhini; Ania Wisniak; Giovanni Piumatti; Andrew S Azman; Stephen A Lauer; Hélène Baysson; David De Ridder; Dusan Petrovic; Stephanie Schrempft; Kailing Marcus; Sabine Yerly; Isabelle Arm Vernez; Olivia Keiser; Samia Hurst; Klara M Posfay-Barbe; Didier Trono; Didier Pittet; Laurent Gétaz; François Chappuis; Isabella Eckerle; Nicolas Vuilleumier; Benjamin Meyer; Antoine Flahault; Laurent Kaiser; Idris Guessous Journal: Lancet Date: 2020-06-11 Impact factor: 79.321
Authors: Stephen A Lauer; Kyra H Grantz; Qifang Bi; Forrest K Jones; Qulu Zheng; Hannah R Meredith; Andrew S Azman; Nicholas G Reich; Justin Lessler Journal: Ann Intern Med Date: 2020-03-10 Impact factor: 25.391
Authors: Adam J Kucharski; Timothy W Russell; Charlie Diamond; Yang Liu; John Edmunds; Sebastian Funk; Rosalind M Eggo Journal: Lancet Infect Dis Date: 2020-03-11 Impact factor: 25.071
Authors: Joel Hellewell; Sam Abbott; Amy Gimma; Nikos I Bosse; Christopher I Jarvis; Timothy W Russell; James D Munday; Adam J Kucharski; W John Edmunds; Sebastian Funk; Rosalind M Eggo Journal: Lancet Glob Health Date: 2020-02-28 Impact factor: 26.763
Authors: Timothy W Russell; Joel Hellewell; Christopher I Jarvis; Kevin van Zandvoort; Sam Abbott; Ruwan Ratnayake; Stefan Flasche; Rosalind M Eggo; W John Edmunds; Adam J Kucharski Journal: Euro Surveill Date: 2020-03
Authors: Emily S Nightingale; Sam Abbott; Timothy W Russell; Rachel Lowe; Graham F Medley; Oliver J Brady Journal: BMC Public Health Date: 2022-04-11 Impact factor: 4.135
Authors: Matthew J Mears; Michael J Wallace; Jacob S Yount; Lorri A Fowler; Penny S Jones; Peter J Mohler; Loren E Wold Journal: MethodsX Date: 2021-06-30
Authors: Enrico Richter; Doaa Al Arashi; Bianca Schulte; Christian Bode; Benjamin Marx; Souhaib Aldabbagh; Celina Schlüter; Beate Mareike Kümmerer; Johannes Oldenburg; Markus B Funk; Christian Putensen; Ricarda Maria Schmithausen; Gunther Hartmann; Anna Eis-Hübinger; Hendrik Streeck Journal: Transfus Med Hemother Date: 2021-05-25 Impact factor: 3.747