COVID-19 infectious period ranges from 10 to 20 days, study finds

A study yesterday in Infection Control & Hospital Epidemiology found that individuals with mild or no COVID-19 symptoms may be infectious for no more than about 10 days, while those with severe illness may be able to spread the virus for as long as 20 days. The infectious periods align with US Centers for Disease Control and Prevention (CDC) recommendations for isolation time.

An accurate understanding of the infectious period duration is vital for COVID-19 infection control practices, according to the study authors. The meta-analysis reviewed 77 studies worldwide that evaluated duration of viral shedding as detected via replication through polymerase chain reaction.

Patients with more severe illness shed viral RNA for a longer period, with an average shedding duration of 19.8 days (95% confidence interval [CI], 16.2 days to 23.5 days; P < 0.01) compared with 17.2 days for those with mild or moderate illness (95% CI, 14.0 days to 20.5 days; P < 0.01).

"Although the pooled median viral RNA shedding duration from patients with mild/moderate and severe disease do not differ greatly, reports of positive viral cultures through day 20 in severely ill patients support the potential for a prolonged infectious period for sicker patients," the authors note.

The researchers found viral RNA detectable in some patients up to 92 days after symptom onset, but viable virus shedding and infectious period duration appear to be much shorter. "In general, the highest viral loads occur within 1-2 weeks of illness onset, regardless of symptoms, with a subsequent gradual decline," the authors found.

The studies reviewed in the analysis differed widely, making generalizations difficult and pointing to the need for additional data, but the analysis confirms previously understood infectious period duration and isolation guidelines.

"Even though people can shed virus for a prolonged period of time, the studies we reviewed indicated that live virus, which may predict infectiousness, was only detected up to nine days in people who had mild symptoms," said co-author Monica Sikka, MD, in an Oregon Health & Science University news release.  
Oct 20 Infect Control Hosp Epidemiol study
Oct 20 Oregon Health & Science University news release

CWD detected at deer farm in another Minnesota county

Chronic wasting disease (CWD) has been detected at a white-tailed deer farm in another Minnesota county, Houston, located in the southeastern part of the state, the Minnesota Board of Animal Health said in a recent statement.

CWD was detected in routine tests in farmed cervids that die or are slaughtered and was found in a 2 ½-year old doe that died. The rest of the herd was quarantined, and the farm's owner is cooperating with animal health officials on tracking animal movements over the last 5 years.

The farm has 38 adults and 11 fawns. The herd was double fenced in 2017, before the board established Houston County as an endemic area in 2018. Over the past 5 years, the farm only imported deer from two Minnesota herds, and the animal that tested positive was imported from a Winona County herd that is also under quarantine. The Houston County herd has only exported deer to one location in Wisconsin.

The Minnesota Department of Natural Resources (DNR) is testing hunter-harvested wild deer in Houston County as part of its fall deer hunting surveillance plan. Michelle Carstensen, PhD, the DNR's wildlife health program supervisor, said officials typically heighten surveillance in areas that surround CWD-infected cervid farms. Given the new detection, she encouraged hunters in the area to submit samples, given that sampling is voluntary this year, due to COVID-19 concerns.
Oct 15 MBAH statement