In a report published online in The New England Journal of Medicine, researchers found that campers spread COVID to household members after returning home ― but transmission was more likely from some than others. Distancing and masking helped reduce the risk.
Victoria T. Chu, MD, with the CDC in Atlanta, Georgia, and colleagues with the agency and the Georgia Department of Health followed up with 224 camp attendees, aged 7 to 19 years, who had evidence of SARS-CoV-2 infection on laboratory testing.
These index patients — 88% of whom had symptoms — had 526 household contacts, mainly parents and siblings. Of 377 household contacts who underwent testing, 46 (12%) tested positive. Another two cases in household contacts were identified using clinical and epidemiologic criteria.
Family Members Hospitalized
Of the 41 adult household contacts who were infected, four (about 10%) were hospitalized. Their hospital stays ranged from 5 to 11 days. Of the seven infected household contacts who were younger than 18 years, none were hospitalized.
The four hospitalized adults were parents and grandparents aged 45 to 80 years, Chu said. Two of the four had underlying conditions. None of the household contacts died.
In an adjusted analysis, campers who had practiced physical distancing were less likely to transmit the virus at home, compared with those who had not practiced physical distancing. Household members who had had close or direct contact with the index patients were more than 5 times more likely to become infected, compared with family members with minimal or no contact, analyses showed.
"This retrospective study showed that the efficient transmission of SARS-CoV-2 from school-age children and adolescents to household members led to the hospitalization of adults with secondary cases of Covid-19," the researchers wrote. "In households in which transmission occurred, half the household contacts were infected."
The secondary attack rates in this report may be an underestimate because testing was voluntary and participants reported the results themselves, the authors noted. It is possible that infected household contacts spread the virus further, but this study did not address that question, Chu said.
For the study, investigators interviewed all camp attendees and their parents or guardians by phone between July 17, 2020, and August 24, 2020, to collect information about demographic and clinical characteristics, SARS-CoV-2 testing, and preventive measures. The researchers' analysis excluded households in which illness onset in a household contact occurred before or less than 2 days after a camper became sick.
About a third of the index patients began to have symptoms while still at camp. These campers may have been less infectious by the time they got home, compared with those whose symptoms started after they returned.
Two thirds of the index patients adopted physical distancing at home, which "probably reduced the transmission of SARS-CoV-2 in the household," Chu and colleagues wrote.
"Children who have had a known COVID-19 exposure should quarantine and obtain testing if they develop symptoms within the 14 days of returning home," Chu advised. "If a child develops COVID-19, the child should be cared for and monitored using the proper combination of physical distancing, isolation when feasible, and mask use to prevent household transmission as much as possible. In addition, any person over the age of 12 is now eligible for vaccination in the United States. If eligible, children attending camp and their family members should get vaccinated to protect themselves and others, as vaccinations are our most effective public health prevention strategy."
Mitigation Can Help
Another report regarding four overnight camps in Maine — in which three campers tested positive after they arrived last summer — shows that "aggressive mitigation strategies can be effective" in limiting transmission of the virus, William T. Basco, Jr, MD, said in a commentary on Medscape Medical News.
This summer, a range of factors, including vaccination rates at the camp, may influence transmission dynamics, Chu tells Medscape Medical News. In July, the Associated Press reported outbreaks tied to summer camps in several states.
"Transmission dynamics will probably vary from summer camp to summer camp depending on many factors, such as vaccination rates of camp attendees, the mitigation measures in place, and the number of individual introductions during camp," Chu says. "We would expect that a camp with a low vaccination rate among attendees and no enforcement of mitigation measures" still may experience a large outbreak.
"On the other hand, a large proportion of vaccinated individuals and appropriate implementation of multiple mitigation measures, such as wearing masks, may be quite effective at keeping their transmission rates low," Chu says. "For camps with younger children who are not currently eligible for vaccination, implementing layered prevention strategies (eg, mask use, physical distancing, and encouraging outdoor activities when feasible) is important to prevent transmission."
Although COVID-19 transmission from children to adults, potentially leading to hospitalization, is not a new phenomenon, "data on the extent of transmission driven by children and adolescents in different settings are still quite sparse," Chu says. "A better understanding of their impact on household and community transmission to help guide public health recommendations is particularly important, as most children are still not eligible for vaccination, and in-person schools will be reopening this fall."