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Household transmission in people infected with SARS-CoV-2 (COVID-19) in Metropolitan Lima

Our take —

This was a surveillance study performed by the National Institute of Health in Peru that included 52 households throughout metropolitan Lima. Upon serological antibody testing, most households (40) had secondary infections. A little more than half of the household contacts were positive for antibodies, with all having a presence of IgM, indicating recent infection. The secondary attack rate (53%) is higher than what has been reported in other studies from China or the U.S. (e.g. 4-17%). These findings could indicate other issues concerning the lack of the ability to socially isolate within households, greater household density, or lack of public health guidelines to prevent transmission in the community. Also, there is a chance that some of the secondary cases obtained the virus through community spread as opposed to through their household. Overall, this is one of the first studies to examine secondary attack rates in Latin America, and thus will be useful in identification of indicators that may put Latin Americans at elevated risk for infection.

Study design

Retrospective Cohort

Study population and setting

The National Institute of Health (INS) in Peru conducted a surveillance study of 52 households with one known confirmed SARS-CoV-2 case in each household from April 23 to May 2, 2020 in metropolitan Lima. The study population includes the entirety of contacts who had available epidemiological data and serological test results (i.e. IgM/IgG) collected by INS, thus, investigators consider the study to be a census. To select these 52 households, investigators evaluated 10 households in each of the four health districts (the Directorates of Integrated Health Networks or DIRIS in Spanish) with the lowest burden of disease as they believed that transmission in these regions would be the result of household contacts as opposed to community spread. They additionally evaluated 10 households that were the district with the highest burden of disease. Investigators collected sociodemographic and clinical characteristics (e.g. presence of symptoms or chronic health conditions) through interviews. They also conducted antibody (IgM and IgG) testing and SARS-CoV-2 infection was defined as the presence of antibodies among those who did not previously test positive. In order to assess validity of the antibody testing, investigators re-evaluated 10 houses using Coretests COVID-19 IgM/IgG Ab Test (Core Technology Co. Ltd).

Summary of Main Findings

Investigators obtained data from 326 people (including 236 contacts) from the 52 households, among whom 37.3% had some kind of pre-existing or risk condition (e.g. age older than 60 years or chronic health condition). The most common conditions were age older than 60 years (39.8%, n=35), hypertension (22.7%, n=20), and bronchial asthma (15.9%, n=14). Most contacts (68.6%) reported symptoms with 49.4% of those reporting a sore throat, and 41.4% reporting fever or cough. Out of the 52 selected households, 40 (77%) households had secondary cases. Fifty-three percent (n=236) of household contacts were positive for antibodies with 110 reacting to both IgM and IgG antibodies and 15 being positive for only IgM. The presence of IgM antibodies in all of the cases indicates that most were recently infected. Most secondary cases (77.6%) were symptomatic. There was an average density of 4.5 people (+/-2.5) per household with 54.1% of members being women, 34.7% of members having a risk condition, and 39.4% were symptomatic secondary cases. Among the houses that were re-evaluated approximately 30 days after the first evaluation, all of the antibody-positive patients that were cases in the first evaluation were still positive in the second evaluation. There were three new cases that occurred in the second evaluation.

Study Strengths

This study has rich, socio-demographic data on secondary household contacts that is not present in many other articles reporting secondary household attack rates.


Investigators used a convenience sample, thus the results may not be representative of the overall population. Relying on antibody testing may also make it more difficult to ensure that household contacts did not acquire the virus through community spread as the timing of exposure is potentially further in the past than if the case were PCR positive. Also, the cases that were deemed to be asymptomatic could very well be pre-symptomatic cases, thus the differences between symptomatic vs. asymptomatic cases may be overrepresented.

Value added

This study is one of few detailed studies concerning the nature of household contacts in Latin America and provides useful information for future investigations evaluating SARS-CoV-2 transmission in households. The secondary attack rates and proportion of symptomatic cases also appears to be higher than prior articles reporting from other countries.

This review was posted on: 16 October 2020