Study population and setting
The study objective was to characterize the rate of transmission of SARS-CoV-2 from primary cases to household contacts. From March 22 to April 22, 2020 in Milwaukee, Wisconsin, and Salt Late City, Utah metropolitan areas. Households were identified through routine public health surveillance, and 198 household contacts who had not been hospitalized prior to or during their 14-day observation period in the study were enrolled. Of these, 3 withdrew for a final study size of 195. Household contacts were interviewed with standardized questionnaire for sociodemographic, clinical, and symptom characteristics at baseline. Nasopharyngeal swabs were taken at baseline and at the end of 14 days and tested for SARS-CoV-2. Daily temperatures were taken and symptoms recorded in a daily diary.
Summary of Main Findings
Of the 195 participants, 47 (24.1%) tested positive using RT-PCR at either baseline or day 14 follow-up. 42 of these contacts (89%) were positive at baseline, and 5 (11%) were initially negative and tested positive at follow-up. 148 (75.9%) remained negative throughout the study period. Upper respiratory symptoms were the most commonly reported among the positive contacts (68%, N=32), as well as neurologic symptoms (64%, N=30). At baseline, 43% of the final participants testing positive reported a cough (N=20), which increased to 74% (N=35) by the end of follow-up. About half reported having a fever (N=25, 53%) or gastrointestinal symptoms (N=25, 53%) at any time during follow-up. Symptom distribution significantly varied by age (p-value = 0.03): Children <18 years and adults >50 years most commonly reported upper respiratory symptoms, while adults 18 – 49 years most commonly reported neurologic symptoms. The study reported no asymptomatic cases at the end of the study period (e.g., everyone either had had symptoms prior or went on to have symptoms).
The study had prospective follow-up of confirmed household contacts with continued testing through the study period to identify seroconverters. Additionally, with the symptom diaries, it was possible to look at time trends over the course of illness among people who had all been exposed because of household contact. The study also presents the trajectory of the contacts who were seronegative at baseline and converted during follow-up, which shows the different symptom types and their recurrence.
The study may suffer from information bias because all symptoms were assessed via self-report. Additionally, by only testing on the first and last day of the follow-up period, it is not possible to tell when exactly seroconversion may have occurred. The study did not clearly describe its sampling strategy, but states that contacts were selected by convenience sample, which would be unlikely to be representative of the US as a whole and may suffer from selection bias.
The study shows the natural symptom progression among household contacts who have test positive for SARS-CoV-2, including seroconverters who developed the disease during follow-up.
This review was posted on: 13 October 2020