Coronavirus disease (COVID-19) in children is known to occur mainly from family clusters (1). However, children can be the only infected members in a household, especially when COVID-19 is contracted from relatives or teachers. Such situations raise concerns about isolation because little information is available on transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19, during colocation of young children with their uninfected guardians. Although children generally are asymptomatic or have mild symptoms, they could be infective (1,2). We explored whether SARS-CoV-2 was transmitted from children to their uninfected guardians in a hospital isolation setting.

During February 18–June 7, 2020, we analyzed all children <19 years of age with COVID-19 and their uninfected guardians who were isolated together in 7 hospitals in South Korea. The infected children were encouraged to wear face masks. The guardians were advised to wear personal protective equipment (PPE), but the degree of PPE varied among hospitals. Adherence to PPE was monitored by the medical staff; compliance was judged as good when PPE was worn most of the time, fair for frequent adherence, and poor when PPE was worn for less than half of the observed time. Children’s isolation was lifted when 2 consecutive negative respiratory samples were obtained >24 hours apart. To ascertain secondary transmission, guardians’ respiratory samples were tested for SARS-CoV-2 if symptoms developed, before their child’s isolation was lifted, and 2 weeks after the end of isolation. This study was approved by the institutional review board of each hospital and written informed consent was waived.

Among 94 children with COVID-19 isolated in 7 hospitals, 12 children were isolated with a single uninfected guardian (Table). The median age of the patients was 6 years (range 2 months–11 years), and children were isolated for a median of 17 days (range 7–37 days). Most (7/12) children were asymptomatic, 4 had fever or respiratory symptoms, and 1 had pneumonia. Only 4 children cooperated well with wearing face masks.

The guardians included 10 mothers, 1 father, and 1 uncle; all complied with wearing PPE (Table). Most (10/12) guardians wore gloves and masks, either KF94 masks, which filter »94% of particles of 0.4 μm in size, or N95 masks which filter »95% of particles of 0.3 μm in size; 7 also wore gowns or coveralls. One guardian used a surgical mask and 1 guardian wore a KF80 mask, which filters »80% of particles of 0.6 μm, and gloves. Most (10/12) guardians had frequent close contact, but 2 children kept a distance of >1 m from their guardians during isolation. None of the guardians were SARS-CoV-2–positive during the study.

For comparison, we also analyzed 2 cases in which adults with COVID-19 were isolated with their uninfected children because no other caregivers were available (Appendix). The adult patients always wore face masks, but the 2 children never wore PPE and always had physical contact with their parents. However, the children did not become infected. The infected parents’ adherence to the use of masks likely aided in curbing SARS-CoV-2 transmission to their uninfected children by reducing virus particles in respiratory droplets (3).

Appropriate use of PPE, especially face masks, might have protected uninfected guardians in our study. Previous reports have emphasized the use of face masks to prevent SARS-CoV-2 transmission in healthcare and community settings (4). Considering the decreased risk for virus transmission noted with PPE, guardians should be counseled on the proper use of PPE when in isolation with infected children.

We did not observe SARS-CoV-2 transmission from children to guardians in isolation settings in which close proximity would seem to increase transmission risk. Recent studies have suggested that children are not the main drivers of the COVID-19 pandemic, although the reasons remain unclear (5). A large study on contacts of COVID-19 case-patients in South Korea observed that household transmission was lowest when the index case-patient was 0–9 years of age (6). Among pediatric cases, the secondary attack rate from children to household members was estimated to be only 0.5% (7). Reduced transmission from children in households was also reported in Switzerland and China and in educational settings in Australia (8–10).

This study is limited by its small sample size, which limits the ability to generalize its results. Moreover, we did not assess the patients’ viral load, which could indirectly reflect the infectivity of the children, nor did we assess patient serology, which could further ascertain their infection status. Despite these limitations, our study provides information on SARS-CoV-2 transmission from children to guardians in isolation rooms. Additional assessments of the transmissibility of SARS-CoV-2 by children and the role of PPE in preventing infection could provide guidance during the ongoing pandemic. Nonetheless, our study adds to growing evidence that young children are less likely to contribute to the spread of COVID-19 among their adult guardians.

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