Estimation of the severeness rate, death rate, household attack rate and the total number of COVID-19 cases based on 16 115 Polish surveillance records

Abstract

Background: Estimating the actual number of COVID-19 infections is crucial for steering through the COVID-19 pandemic crisis. It is, however, notoriously difficult, as many cases have no or only mild symptoms. Surveillance data for in-household secondary infections offers unbiased samples for COVID-19 prevalence estimation. Methods: We analyse 16115 Polish surveillance records to obtain key figures of the COVID-19 pandemic. We propose conservative upper and lower bound estimators for the number of SARS-CoV-2 infections. Further, we estimate age-dependent bounds on the severe case rate, death rate, and the in-household attack rate. Results: By maximum likelihood estimates, the total number of COVID-19 cases in Poland as of July 22nd, 2020, is at most around 13 times larger and at least 1.6 times larger than the recorded number. The lower bound on the severeness rate ranges between 0.2% for the 0-39 year-old to 5.7% for older than 80, while the upper bound is between 2.6% and 34.1%. The lower bound on the death rate is between 0.04% for the age group 40-59 to 1.34% for the oldest. Overall, the severeness and death rates grow exponentially with age. The in-household attack ratio is 8.18% for the youngest group and 16.88% for the oldest. Conclusions: The proposed approach derives highly relevant figures on the COVID-19 pandemic from routine surveillance data, under assumption that household members of detected infected are tested and all severe cases are diagnosed.

Household Transmission of SARS-CoV-2

“…Figure 1 summarizes secondary attack rates for 44 studies [19][20][21][22][23][24][25][26][28][29][30][32][33][34][35][36][38][39][40][41][42][43][44][45][47][48][49][50][51][52][53][54][55][56][57]59,[61][62][63][65][66][67]69,70 of household contacts and 10 of family contacts. 26,31,37,45,58,60,65,68,…”

“…No significant publication bias was observed for studies of household, family, or close contacts (eFigure 3 in the Supplement). Secondary attack rates were not significantly different when restricting to 38 studies 19,20,22,23,[26][27][28][29][30][31][34][35][36][37][38][39][40]42,[44][45][46][47][48][49][50][51][54][55][56][57]60,62,63,65,[67][68][69]72 with low or moderate risk of bias (15.6%; 95%, 12.8%-18.5%) (eFigure 4 in the Supplement). There were no significant differences in secondary attack rates between 21 studies in China 22,27,31,36,37,39,45,46,48,58,[61]...…”

“…studies that tested symptomatic contacts [19][20][21]24,25,28,29,33,34,41,47,50,53,56,58,59,61,64 and 33 studies that reported testing all contacts 22,23,26,27,30,31,[35][36][37][38][39][40][42][43][44][45][46]48,49,51,52,54,55,57,60,63,[65][66][67][69][70][71][72] (eFigure 6 in the Supplement), and 16 early studies 22,…”

“…To study the transmissibility of asymptomatic SARS-CoV-2 index cases, eFigure 8 in the Supplement summarizes 27 studies [19][20][21][23][24][25][26]30,[32][33][34]44,45,47,50,[52][53][54]56,[59][60][61]63,64,68,69,72 reporting household secondary attack rates from symptomatic index cases and 4 studies 26,43,44,52 from asymptomatic or presymptomatic index cases. Estimated mean household secondary attack rate from symptomatic index cases (18.0%; 95% CI, 14.2%-22.1%) was significantly higher than from asymptomatic or presymptomatic index cases (0.7%; 95% CI, 0%-4.9%; P < .001), although there were few studies in the latter group.…”

“…Furthermore, many analyses ignored tertiary transmission within the household, classifying all subsequent cases as secondary to the index case. Eighteen studies [19][20][21]24,25,28,29,33,34,41,47,50,53,56,58,59,61,64 involved testing only symptomatic household contacts, which would miss asymptomatic or subclinical infections, although secondary attack rate estimates were similar across studies testing all vs only symptomatic contacts. Important questions remain regarding household spread of SARS-CoV-2.…”