Patients with COVID-19 outside of Wuhan, China, shed the virus for a median of 17 days, according to a retrospective cohort study published in the International Journal of Infectious Diseases.
Also, a study in the same journal found that third-generation transmission of the COVID-19 epidemic likely began on Jan. 17 to 20 in Wuhan, then spread to the rest of Hubei province from Jan. 23 to 24, while the mixed first- and second-generation transmissions interacted to worsen the outbreak.
In the first study, researchers studied the clinical factors, lab results, treatments, and outcomes of 147 adult COVID-19 patients in a single hospital in Changsha, China, the capital of Hunan province, which is adjacent to Hubei province.
· Fever at hospital admission, longer time from symptom onset to admission, and lengthier hospital stay were associated with longer periods of viral shedding.
· Median time from symptom onset to admission was 6 days (interquartile range, 3 to 10). Of the 147 patients, 127 (86%) had moderate illness, while 20 (14%) had severe illness. Length of viral shedding ranged from 6 to 47 days.
· No patients required advanced respiratory support or died. Age, sex, body mass index (BMI), history of exposure, and underlying illnesses were not significantly different between 82 patients who shed virus for less than 17 days and the 65 who shed virus longer than that.
· The viral load in patients who shed virus for less than 17 days was undetectable for 15 of 30 patients 12 days after symptom onset, while it took 22 days for the viral load in 16 of 31 patients with prolonged viral shedding to clear the virus.
· The median patient age was 42 years, and 54% were female. Median BMI was 23.2 kg/m2. Seventy-three patients had been exposed to other COVID-19 patients, while 113 of 147 patients (77%) were associated with a family cluster.
· Thirty of 147 patients (20%) had one or more underlying diseases. The most common symptoms were fever (115 of 147 [78%]), cough (122/147 [83%]), and fatigue (62/147 [42%]). All but six patients had abnormal chest radiography findings, 85% (124 of 147) with bilateral lung involvement. Patients with prolonged shedding also had significantly lower arterial oxygenation and higher iron levels than other patients.
The authors said that the identified risk factors for prolonged viral shedding should be considered when formulating strategies for quarantine and called for a large, multicenter study to further explore these factors.
In the second study, researchers using space-time data from COVID-19 cases in mainland China and mobile device data detected no third-generation spread of the novel coronavirus outside of Hubei.
First-generation, or primary, disease transmission was reflected in movement from the Wuhan seafood market, and second-generation, or secondary, transmission was reflected in travel from Wuhan city to elsewhere in Hubei. Third-generation, or tertiary, transmission is usually caused by local rather than imported cases.
They noted that several million travelers from Wuhan left the city for the annual Chinese New Year holiday in the first half of January, and the first case of COVID-19 outside of Hubei was reported on Jan. 19. The outbreak spread rapidly over the next three or four days, despite strict transportation screening procedures implemented in many cities. First- and second-generation spread occurred at the same time in many cities early in the epidemic, enhancing the spread.
The authors said their findings provide a clearer picture of the effect of human movement on epidemic transmission and identify important current and future containment measures. "The associations between the epidemic spread decreased with distance and had different temporal patterns from the epidemic sources, implying the potential epidemic generation-to-generation evolution on regional spatial scales," they said.
They proposed control measures of different levels could vary by location and time in different areas, with cities with third-generation transmission enacting the strictest controls on both those in quarantine and exported cases, and cities with simultaneous first- and second-generation transmission focusing on those in quarantine and imported cases. Other cities could focus on controlling imported cases.
"More attention should be given to control of the trend of second-generation spread and to eliminate potential third-generation spread," they wrote.
