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Transmission of SARS-COV-2 Infections in Households: CDC via MMWR, October 30, 2020

2020-10-30
SARS-COV-2 EM photo courtesy NIAID

The Centers for Disease Control (CDC) published a Morbidity and Mortality Weekly Report (MMWR) on October 30, 2020 titled “Transmission of SARS-COV-2 Infections in Households– Tennessee and Wisconsin, April-September 2020.” This report states that 102 of 191 contacts of 101 patients with positive RT-PCR (reverse transcriptase polymerase chain reaction) tests for SARS-COV-2 developed positive RT-PCR tests during follow-up. The secondary infection rate was 53%.

From the report:

For this analysis, 101 households (including 101 index patients and 191 household members) were enrolled and completed ≥7 days of follow-up. The median index patient age was 32 years (range = 4–76 years; interquartile range [IQR] = 24–48 years); 14 (14%) index patients were aged <18 years, including five aged <12 years and nine aged 12–17 years. Among index patients, 75 (74%) were non-Hispanic White, eight (8%) were non-Hispanic persons of other races, and 18 (18%) were Hispanic or Latino (Table 1). Index patients received testing for SARS-CoV-2 a median of 1 day (IQR = 1–2) after illness onset and were enrolled in the study a median of 4 days (IQR = 2–4) after illness onset.

The median number of household members per bedroom was one (IQR = 0.8–1.3). Seventy (69%) index patients reported spending >4 hours in the same room with one or more household members the day before and 40 (40%) the day after illness onset. Similarly, 40 (40%) of index patients reported sleeping in the same room with one or more household members before illness onset and 30 (30%) after illness onset.

Among all household members, 102 had nasal swabs or saliva specimens in which SARS-CoV-2 was detected by RT-PCR during the first 7 days of follow-up, for a secondary infection rate of 53% (95% CI = 46%–60%) (Table 2). Secondary infection rates based only on nasal swab specimens yielded similar results (47%, 95% CI = 40%–54%). Excluding 54 household members who had SARS-CoV-2 detected in specimens taken at enrollment, the secondary infection rate was 35% (95% CI = 28%–43%).

Forty percent (41 of 102) of infected household members reported symptoms at the time SARS-CoV-2 was first detected by RT-PCR. During 7 days of follow-up, 67% (68 of 102) of infected household members reported symptoms, which began a median of 4 days (IQR = 3–5) after the index patient’s illness onset. The rates of symptomatic and asymptomatic laboratory-confirmed SARS-CoV-2 infection among household members was 36% (95% CI = 29%–43%) and 18% (95% CI = 13%–24%), respectively.

https://www.cdc.gov/mmwr/volumes/69/wr/mm6944e1.htm

The report states that, “About 75% of secondary infections were identified within 5 days of the index patient’s illness onset.” As noted in the excerpt above, 54 of the household members were already infected at the time the index patient was enrolled, that is, nearly simultaneously. The report gives recommendations for immediate self-isolation and mask-wearing for all household members. However, that would be too late for those 54 patients.

The data presented in this report are from an ongoing study in two locations: Nashville, Tennessee and Marshfield, Wisconsin. Additional information from this study is likely to be forthcoming.

The study shows that household infections occur commonly and quickly after a member of the household brings home the virus. This makes it imperative for control of this virus that everyone in an affected household be aware of infection status for household members and take appropriate precautions at once.

The CDC is still functioning despite attempts by this administration to undermine and politicize it. This study shows that it is still producing important science and publicizing it to everyone who will listen.

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