Effectiveness of isolation and contact tracing for containment and slowing down a COVID-19 epidemic: a modelling study

Mirjam E Kretzschmar; Ganna Rozhnova; Michiel E van Boven

(which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.03.10.20033738 doi: medRxiv preprint An infectious individual makes contacts with household members and persons outside the 156 household. We model the daily number of household contacts with a Poisson distribution, 157 and the numbers of non-household contacts with a negative binomial distribution (Table 1) , 158 with parameters based on the average household size in the Netherlands, and numbers of 159 contacts observed in a contact study in the Netherlands (FigureS1b) [20] . With the chosen 160 parameters, the mean number of contacts per day is 13.2 (SD 8.5). 161 On each day of the infectious period, an individual makes a number of contacts according to 162 the contact distribution. This number is reduced by a factor describing the probability that 163 the contact person has already been infected during earlier contacts with the index person. 164 More precisely, the number of contacts is reduced by a factor fk per day k of the infectious 165 period, describing the probability that a contact has already been infected on previous days 166 of the infectious period of the index case. The probability of transmission upon contact with 167 a susceptible household contact is given by the distribution in Figure S1a . As contacts with 168 persons outside the household are often less close, we assume that the transmission 169 probability for these contacts is lower by factor 0.25. Figure CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.