More than half of residents of a Seattle-area nursing home had no symptoms when they tested positive for COVID-19 and had probably already spread the disease, according to a study published late last week in the New England Journal of Medicine (NEJM).Also, a study in Emerging Infectious Diseases (EID) found that all five household contacts of a mildly symptomatic doctor in Wuhan, China infected with the novel coronavirus had the disease but no symptoms.Shortcomings of symptom-based screening, cohortingIn the NEJM study, officials with Public Health–Seattle and King County and the Centers for Disease Control and Prevention conducted two serial point-prevalence surveys 10 and 17 days after an outbreak was identified at the nursing home in