CDC study finds household COVID-19 transmission common
New data released today in Morbidity and Mortality Weekly Report (MMWR) show that household transmission of SARS-CoV-2, the virus that causes COVID-19, is common, occurs early after illness onset, and can originate from both children and adults.
In a study conducted among households in Nashville, Tennessee, and Marshfield, Wisconsin, researchers from the Centers for Disease Control and Prevention and their partners enrolled 101 households (including 101 index patients and 191 household members) and asked participants to document their symptoms and obtain self-collected specimens for 14 days. The researchers then tested specimens from the first 7 days for SARS-CoV-2.
Index patients received SARS-CoV-2 testing a median of 1 day after illness onset and were enrolled in the study a median of 4 days after onset. Sixty-nine percent of index patients reported spending more than 4 hours in the same room with one or more household members the day before illness onset, and 40% the day after illness onset.
Overall, 102 household members tested positive during the first 7 days of follow-up, for a secondary infection rate of 53%. Excluding household members who had SARS-CoV-2 detected in specimens taken at enrollment, the secondary infection rate was 35%. Substantial secondary transmission occurred regardless of index patient age: 53% for index patients under 12, 38% for those aged 12 to 17 years, 55% for 18 to 49 year-olds, and 62% for those over 50.
Approximately 75% of infections were identified within 5 days of the index patient's illness onset. Forty percent of infected household members reported no symptoms at the time SARS-CoV-2 was detected, while 67% of household members reported symptoms over 7 days of follow-up. The rates of symptomatic and asymptomatic transmission were 36% and 18%, respectively.
"Persons who suspect that they might have COVID-19 should isolate, stay at home, and use a separate bedroom and bathroom if feasible," the authors wrote. "Isolation should begin before seeking testing and before test results become available because delaying isolation until confirmation of infection could miss an opportunity to reduce transmission to others."
The authors also suggest that all household members, including the index patient, start wearing a mask in shared spaces in the home during this period.
Oct 30 CDC MMWR study
Review suggests higher transmission in older schoolchildren
A literature review today in The Journal of Infectious Diseases found that SARS-CoV-2 appeared to have a more limited spread in primary schools compared with secondary/high schools, although mitigation measures and community case levels were also factors. The researchers also found that children under 10 years old appeared to be relatively less susceptible to SARS-CoV-2 infection and that serologic prevalence may be higher in younger adults under 35.
The authors, from Harvard University and the University of St. Andrews in Britain, included in their review 14 studies that looked at how susceptibility, infectivity, and seroprevalence differed across age-groups.
"Some uncertainty remains about the magnitude of the difference in susceptibility of children vs. adults due to presence of biases in several published studies," the researchers write. "On the other hand, comparisons between younger and older children are arguably more robust and—in the one study that reports them—reach the same conclusion."
Regarding school outbreaks, the researchers looked at papers published prior to Oct 6 on the Living Evidence on COVID-19 database and found that multiple outbreaks were linked to school transmission, not just community caseloads. Studies found that factors like limited mask use, normal/crowded class sizes, and limited testing and quarantine contributed to larger outbreaks.
In one outbreak in Baden-Würtemberg, Germany, officials were able to limit further infection despite not mandating face masks. Instead, the school followed other safety guidelines, such as halving group sizes, and the school had only 6 of 137 infected children spread COVID-19 to a total of 11 other school contacts. In a Salt Lake County, Utah, assessment, masks were mandated at schools, and the vast majority of outbreaks were under 15 cases, with the exception of a few larger outbreaks that were mostly centered around high schools.
To help prevent school outbreaks, the researchers recommend that schools adhere to World Health Organization guidelines for both students and staff and be particularly careful when opening secondary/high schools.
Oct 29 J Infect Dis study
Study notes 36% rate of COVID-19 in New York City emergency workers
From Mar 1 through May 31, 5,175 out of 14,290 (36.2%) firefighters and emergency medical workers with the Fire Department of the City of New York (FDNY) had confirmed or suspected COVID-19 infections, according to a study today in ERJ Open Research.
Compared with the general New York City population, which had a 2.4% infection rate during the same period, these frontline workers were 15 times more likely to be infected. Still, the number of severe cases in FDNY frontline workers was lower than the general population, possibly due to the "healthy worker effect": 62 cases (1.2%) were classified as severe and 4 (0.08%) were fatal.
FDNY emergency health workers were 26% more likely to have a confirmed COVID-19 case and a 4.23-fold increased likelihood of developing severe outcomes compared with firefighters, the study found. The researchers suggest this could be attributed to prolonged on-the-job contact with people (eg, sharing ambulance transportation, intubation procedures). Generally, the emergency medical workers were more likely to be younger than the firefighters (mean, 38.7 years vs 41.0), female (29.3% vs 1.1%), and of a non-white race or ethnicity (60.7% vs 22.9%).
Smoking habits did not seem to affect COVID-19 infections in this study, although deteriorating lung health (a decline in forced expiratory volume) increased the risk of severe COVID-19 infection by 71%. The data also revealed that minority race was strongly associated with COVID-19 hospitalizations, similar to other studies.
"These findings highlight the importance of protecting emergency workers in countries around the world and maintaining the capacity of our emergency services," said David Prezant, MD, senior author and FDNY chief medical officer, in a European Lung Foundation news release.
Oct 29 ERJ Open Res study
Oct 29 European Lung Foundation press release
