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

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Describe the characteristics of SARS-CoV-2 infection among household members with a confirmed primary case of COVID-19 in low burden districts in Metropolitan Lima.

Materials and Methods

A retrospective, secondary database review study was conducted. The information was collected from an epidemiological surveillance activity in close contacts (co-inhabitants) in 52 households in Metropolitan Lima with only one member with COVID-19. A reevaluation was carried out in 10 households. Epidemiological and clinical variables were evaluated and its association with the result of the rapid serological test (presence of IgG, IgM or both).


Secondary cases were found in 40 households, which represents an average of 49.9% identification per household. A secondary attack rate of 53.0% (125 cases) was found among cohabitants, with 77.6% of cases being symptomatic (symptomatic / asymptomatic ratio: 3.5). The presence of fever and / or chills was found in 40.0% of people with a positive result, followed by a sore throat, in 39.2%. Ageusia and anosmia were present in 22.4% and 20.8% of cases, respectively. A reevaluation in 40 family members 33.6 ± 2.7 days after the first evaluation, show the persistence of positive IgM and IgG in the 20 positive cases in the first evaluation.


Having a primary case of COVID-19 in home, the secondary attack rate of this infection is 53%; however, in a significant proportion of households evaluated there was no positive case, beyond the primary case. The epidemiological and clinical characteristics found in this case were in accordance with what has already been reported in other international series.

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  1. SciScore for 10.1101/2020.09.06.20189456: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementConsent: Ethical aspects: Due to the use of secondary data analysis for this study, in the context of an activity of epidemiological surveillance, an informed consent was no required.
    IACUC: The study has the approval of the Institutional Ethics Committee for Research from the National Institute of Health (RD N°256-2020-OGITT/INS).
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    The serological test used was Coretests ® COVID-19 IgM / IgG Ab Test (Core Technology Co. Ltd), a lateral flow immunochromatographic test that qualitatively detects the presence of antibodies against SARS-CoV-2, with a sensitivity and specificity reported by the manufacturer for IgM / IgG of 97.6% and 100%, respectively.
    COVID-19 IgM / IgG
    suggested: None
    suggested: None
    Variables: The study considers a main variable called SARS-CoV-2 infection, and defined as the presence of antibodies (IgM, IgG or both) in people who had not previously being tested with a positive result (RT-PCR or serological test).
    IgM, IgG
    suggested: None
    Software and Algorithms
    16.0 (Stata Corporation, College Station, Texas, USA ®), and Microsoft Excel 2016 ®.
    Microsoft Excel
    suggested: (Microsoft Excel, RRID:SCR_016137)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    This research has important limitations to consider: the selection of the households in the epidemiological surveillance activity was carried out for convenience, so the results presented cannot be extrapolated to the general population. Likewise, there was no component of temporality for all the cases, which does not allow establishing whether the cases called “asymptomatic” were actually pre-symptomatic cases. The reevaluation activity could not be carried out in all the households initially included, which adds an important selection bias and reduces the external validity of the conclusions that can be obtained from these data. Despite this, due to not finding similar antecedents in Latin America, this study presents results that can serve as a basis for future research that generates knowledge about the dynamics of household transmission of SARS-CoV-2. Although the serological tests used in the study have the endorsement of the state regulatory authority (INS) through laboratory evaluations; in Peru, there is only one field study that uses this type of test for this purpose; however, this research uses another brand (Zhejang Orient Gene ®), and does not define diagnostic performance values. Finally, it is concluded that having a primary case of COVID-19 in the home, the secondary attack rate of this infection is 53%; however, in 23% of the homes evaluated there was no positive cases, beyond the primary case. The epidemiological and clinical characteristics found in this s...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. 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


    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.