Studies show COVID-19 likely has multiple infection routes

Feb. 20, 2020

As the COVID-19 outbreak grows in China and abroad, new studies attempt to answer how the virus is shed and the range of clinical outcomes. Two studies indicate that shedding—and therefore transmission—likely occurs via multiple routes.

Currently, testing for and confirmation of infection with COVID-19 is conducted via oral swabs. But in a study published in Emerging Microbes & Infections, Chinese scientists report evidence of an oral-fecal transmission route for COVID-19 viruses and show that, in hospitalized patients, viral RNA was found in anal swabs and in blood samples.

The study was conducted in a Wuhan, China hospital with samples collected from 178 patients. The study authors found viral nucleotide in anal swabs or blood even when it was not detected in oral swabs, especially in patients who had been receiving supportive care for several days. The results also showed that the timing of positive swabs changed. On the first day of illness, 80% of oral swabs were positive in a small group of patients, but by day five, 75% of anal swabs were positive for COVID-19 viral RNA, and only 50% of oral swabs were still positive in the same patients with lab-confirmed COVID-19.

"These data suggested a shift from more oral positive during early period (as indicated by antibody titers) to more anal positive during later period might happen," the authors said. The results of the study are the first to show COVID-19 could be transmitted via respiratory, fecal-oral, or body fluid routes, the authors say. They also warn that a patient with negative oral swabs after several days of illness may still be capable of transmitting the virus.

In a report from the Chinese Center for Disease Control, authors describe how they isolated the virus from a stool sample of a patient with COVID-19. "Respiratory droplets and contact transmission are considered to be the most important routes of transmission of 2019-nCoV, but do not fully account for the occurrence of all coronavirus disease 2019 (COVID-19) cases, previously known as novel coronavirus pneumonia (NCP), and the reasons for the rapid spread of this virus," they write. The finding suggests stool can contaminate hands, food, water, and, as with the other study, it points to multiple routes of transmission.

In The BMJ, Chinese scientists looked at the clinical findings of 62 COVID-19 patients from seven hospitals in Zhejiang province, China. None of the patients died, and only one patient was admitted to the intensive care unit. Of the 62 patients, 48 (77%) presented with a fever, 50 (81%) had a cough, 35 (56%) had a productive cough, 32 (52%) reported muscle pain or fatigue, and 21 (34%) had a headache. Only two patients (3%) developed shortness of breath on admission, the authors said. They also said that, compared with patients in Wuhan, the patients seen in Zhejiang had relatively mild symptoms. None of the patients had exposure to the Wuhan seafood market linked to the origin of the virus, and all had contracted the disease front another infected person. Patients who experienced symptoms for the more than 10 days were more likely to have underlying health issues.

The authors also provided a timeline for infection: "Among 56 patients who could provide the exact date of close contact with someone with confirmed or suspected SARS-CoV-2 infection, the median incubation period from exposure to symptoms was 4 days (interquartile range 3-5 days). The median time from onset of symptoms to first hospital admission was 2.0 (1.0-4.3) days."

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