january 2021 • Lancet

Household transmission of SARS-CoV-2 and risk factors for susceptibility and infectivity in Wuhan: a retrospective observational study

Fang Li, et al.

DOI: 10.1016/S1473-3099(20)30981-6

Content curated by:David Rodrigues

Key message

Dentro das famílias, crianças e adolescentes foram menos suscetíveis à infecção por SARS-CoV-2, mas revelaram ser mais infecciosos do que indivíduos mais velhos. Os casos pré-sintomáticos foram mais infecciosos e os indivíduos com infecção assintomática menos infecciosos do que os sintomáticos.Verificou-se ainda que após o isolamento em massa de casos, quarentena de contatos domiciliares e políticas de restrição de movimento, os números reprodutivos domiciliares diminuíram.

Analysis

Population

Famílias de todos os casos de COVID-19 confirmados por laboratório ou clinicamente confirmados e infecções assintomáticas por SARS-CoV-2 confirmadas por laboratório identificadas pelo Centro de Controle e Prevenção de Doenças de Wuhan entre 2 de dezembro de 2019 e 18 de abril de 2020

Method

Estudo de coorte retrospectivo. Usaram um modelo de transmissão estatística para estimar as taxas de ataque secundário domiciliar e para quantificar os fatores de risco associados à infectividade e suscetibilidade à infecção, contabilizando o histórico de exposição em nível individual. Avaliamos como as políticas de intervenção afetaram o número reprodutivo domiciliar, definido como o número médio de contatos domiciliares que um caso pode infectar.

Results

A taxa de ataque secundário foi de 15,6% (IC 95% 15,2–16,0) >60 anos em maior risco de infecção Crianças de 0–1 anos de idade eram significativamente mais propensos a serem infectados do que crianças de 2–5 anos e as de 6–12 anos. Dado o mesmo tempo de exposição, crianças e adolescentes com menos de 20 anos de idade tinham mais probabilidade de infectar outras pessoas do que adultos com 60 anos ou mais (1 · 58, 1 · 28–1 · 95). Os indivíduos assintomáticos eram muito menos propensos a infectar outras pessoas do que os casos sintomáticos (0,21,14-0,31). Os casos sintomáticos eram mais propensos a infectar outras pessoas antes do início dos sintomas do que depois (1 · 42, 1 · 30–1 · 55). Após o isolamento em massa de casos, quarentena de contatos domiciliares e políticas de restrição de movimento, os números reprodutivos domiciliares diminuíram 52% entre os casos primários (de 0,25 [IC 95% 0,24-0,26] para 0,12 [0 · 10–0 · 13]) e por 63% entre os casos secundários (de 0,17 [0 · 16–0 · 18] a 0 · 063 [0 · 057–0 · 070]).

Abstract

Background Wuhan was the first epicentre of COVID-19 in the world, accounting for 80% of cases in China during the first wave. We aimed to assess household transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and risk factors associated with infectivity and susceptibility to infection in Wuhan. Methods This retrospective cohort study included the households of all laboratory-confirmed or clinically confirmed COVID-19 cases and laboratory-confirmed asymptomatic SARS-CoV-2 infections identified by the Wuhan Center for Disease Control and Prevention between Dec 2, 2019, and April 18, 2020. We defined households as groups of family members and close relatives who did not necessarily live at the same address and considered households that shared common contacts as epidemiologically linked. We used a statistical transmission model to estimate household secondary attack rates and to quantify risk factors associated with infectivity and susceptibility to infection, accounting for individual-level exposure history. We assessed how intervention policies affected the household reproductive number, defined as the mean number of household contacts a case can infect. Findings 27 101 households with 29 578 primary cases and 57 581 household contacts were identified. The secondary attack rate estimated with the transmission model was 15·6% (95% CI 15·2–16·0), assuming a mean incubation period of 5 days and a maximum infectious period of 22 days. Individuals aged 60 years or older were at a higher risk of infection with SARS-CoV-2 than all other age groups. Infants aged 0–1 years were significantly more likely to be infected than children aged 2–5 years (odds ratio [OR] 2·20, 95% CI 1·40–3·44) and children aged 6–12 years (1·53, 1·01–2·34). Given the same exposure time, children and adolescents younger than 20 years of age were more likely to infect others than were adults aged 60 years or older (1·58, 1·28–1·95). Asymptomatic individuals were much less likely to infect others than were symptomatic cases (0·21, 0·14–0·31). Symptomatic cases were more likely to infect others before symptom onset than after (1·42, 1·30–1·55). After mass isolation of cases, quarantine of household contacts, and restriction of movement policies were implemented, household reproductive numbers declined by 52% among primary cases (from 0·25 [95% CI 0·24–0·26] to 0·12 [0·10–0·13]) and by 63% among secondary cases (from 0·17 [0·16–0·18] to 0·063 [0·057–0·070]). Interpretation Within households, children and adolescents were less susceptible to SARS-CoV-2 infection but were more infectious than older individuals. Presymptomatic cases were more infectious and individuals with asymptomatic infection less infectious than symptomatic cases. These findings have implications for devising interventions for blocking household transmission of SARS-CoV-2, such as timely vaccination of eligible children once resources become available.