Symptomatic patients most likely to spread COVID-19, study says

March 12 (UPI) -- At least 373 people came in contact with a woman who traveled to Wuhan, China, and acquired the new coronavirus, but her husband was the only one she spread it to -- which researchers say suggests exposure to symptomatic patients is the clearest way to get the disease.

While not the only way COVID-19 can be transmitted, the first case of human-to-human transmission in the United States -- involving a married couple in Illinois -- suggests "prolonged" exposure to the virus increases the risk the most for acquiring the disease, a new study has reported.

The study, published Thursday in The Lancet by Illinois public health officials, details how the woman's visit to family in China with a then-undiagnosed respiratory illness led to her showing symptoms 19 days later, before transmitting it to her husband.

The report comes one day after another analysis, also published by The Lancet, revealed that those with confirmed COVID-19 might be contagious for up to 37 days after infection.

A separate study, conducted with the National Institutes of Health, which has not been peer-reviewed or published in a journal, found the virus might remain in the air for up to three hours and survive on contaminated surfaces for as long as two to three days.

The new Lancet report "suggests that person-to-person transmission of SARS-CoV-2 might be most likely to occur through unprotected, prolonged exposure to an individual with symptomatic COVID-19," Jennifer Layden, Chief Medical Officer for the Chicago Department of Public Health, said in a press release.

"Healthcare facilities should rapidly triage and isolate individuals suspected of having COVID-19, and notify infection prevention services and local health departments for support in testing, management and containment efforts," Layden said.

According to the study, public health officials in Illinois immediately conducted an intensive epidemiologic investigation of the two confirmed cases once they were diagnosed.

In all, 372 individuals were identified as potential contacts, and 347 of them were actively monitored after confirmation of exposure on or after the day of symptom onset in the wife and husband. This included 152 "community contacts" -- such as neighbors -- and 195 healthcare professionals.

No evidence of additional transmission after monitoring the close contacts of the couple was found. All of those monitored -- and 75 who were ultimately tested -- remained clear of the virus, including healthcare workers who treated the couple.

Of the 347 who were monitored, 43 developed fever, cough or shortness of breath and were isolated and tested for SARS-CoV-2. In addition, a "convenience sample" of 32 asymptomatic healthcare personnel contacts also were tested. All tested negative for SARS-CoV-2.

The authors of the Lancet report emphasized that their investigation might not have identified all individuals with potential exposure to COVID-19, because "it was dependent on the couples' recall of the places they visited, the people they met, and the time of symptom onset."

In addition, their investigation was conducted before updated U.S. Centers for Disease Control and Prevention guidance on exposure risk among contacts of patients with COVID-19.

"Current CDC recommendations for individuals with high-risk exposures to remain quarantined with no public activities might be effective in reducing onward person-to-person transmission of SARS-CoV-2," Tristan McPherson, an infectious disease specialist at the Chicago Department of Public Health, said in a press release.

According to a study published this week in Annals of Internal Medicine, people infected with COVID-19 are symptom-free for an average of five days after infection. That study reviewed 181 cases from China and other countries that were confirmed before Feb. 24 and determined likely dates of exposure and symptom onset. Most of the cases involved travel to or from Wuhan.

The analysis found that about 98 percent of those who develop symptoms of COVID-19 will do so within 11.5 days of exposure. The findings support the 14-day quarantine period recommended for suspected cases because, for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine, the authors said.

The authors of the new Lancet paper reported that the Illinois woman traveled to Wuhan on Dec. 25 and visited a hospitalized relative and other family members with a then-undiagnosed respiratory illness. She returned to the U.S. on Jan. 13 and experienced six days of mild fever, fatigue and cough before being hospitalized and testing positive for COVID-19.

Both the wife and husband have fully recovered and been discharged to home isolation, which was lifted 33 days after the woman's returned from Wuhan following two negative tests for COVID-19 administered 24 hours apart. The husband also has been declared cured.

"Without using appropriate face masks or other personal protective equipment, individuals living in the same household as, or providing care in a non-healthcare setting for, a person with symptomatic COVID-19 are likely to be at high risk of infection," McPherson said.