Basic Information on the Spread and Course of COVID-19 Infection in China: What We Know So Far?

Epidemiology

The first described cases of acute respiratory infection caused by the new coronavirus in Wuhan were related to exposure at a large seafood market. Soon, cases without this exposure and cases in other countries were identified. According to the National Health Commission, as of March 2, 2020, 80,302 people in China (including Hong Kong and Taiwan) had contracted COVID-19, and 2,947 had died (3.66%). As of that date, 58.85% of patients had recovered. Chinese data also shows that by February 11, 2020, 1,715 healthcare workers had contracted the disease, of whom 5 had died (0.3%). The mortality rate for SARS-CoV-2 is therefore likely lower than for its related coronaviruses SARS-CoV (10%) and MERS-CoV (37%). In Hubei province, whose capital is Wuhan, 0.11% of the population had contracted COVID-19 (36,167 cases out of 59,170,000 inhabitants). Compared with the H1N1 influenza virus, which has the same transmission method, the percentage of the affected population is 50 times lower, highlighting the benefits of the quarantine measures taken.

Source and Transmission

SARS-CoV-2 is the 7th known coronavirus (beta CoV) and was likely transmitted to humans from bats. However, it is possible that the transmission happened through another intermediate host, such as minks or pangolins. Human-to-human transmission was soon confirmed. It is a droplet infection that spreads through direct contact, with asymptomatic infected individuals playing a significant role in its transmission. The virus has also been detected in stool, but it is unlikely that it spreads via the fecal-oral route. Cases of mother-to-newborn transmission have also been reported. The contagiousness factor of the disease (R0 – the number of people one infected person will spread the virus to) varies in different studies: 2.2, 3.1, or 2.0–3.3, with research conducted in the USA even suggesting an R0 of 6.47. It has been found that reducing R0 significantly decreases the cumulative number of cases, emphasizing the importance of quarantine measures.

Incubation Period and Clinical Manifestations

The incubation period is variably reported by Chinese sources: a median of 5.2 days with a range of 4.1–7.0 or a median of 3.0 days with a range of 0–24 days. The median time from the onset of symptoms to the development of shortness of breath is 5 days (1–10), to hospitalization 7 days (4–8), and to the development of acute respiratory distress syndrome 8 days (6–12).

Symptoms are nonspecific and range in severity, from subclinical to severe pneumonia and death. In the study published by Weijie et al., among 1,099 evaluated cases, the most common symptoms were fever (87.9%) and cough (67.7%), followed by fatigue, shortness of breath, headache, hemoptysis, sometimes a runny nose, with 5% of patients vomiting and 3.7% having diarrhea. A quarter of the patients had at least one comorbidity (hypertension, COPD). Lymphocytopenia was found in 82% of patients.

In the study published by Chaolin et al., patients who developed pneumonia were reported. Complications included acute respiratory distress syndrome, acute heart injury, and secondary infections. 32% of these patients required ICU care.

Wang et al. stated in their series of 138 hospitalized patients that those requiring ICU care were older, more often had comorbidities, and experienced shortness of breath more frequently.

Other studies confirm that children have a lower risk of infection, and the disease in children mostly runs asymptomatically.

The Epidemiology Working Group at the Chinese Center for Disease Control and Prevention summarized in their assessment of several tens of thousands of cases that most patients in China were between 30–70 years old and 80.9% had mild pneumonia.

Conclusion

The current worldwide outbreak of COVID-19 infection is caused by the highly pathogenic SARS-CoV-2 virus, which is likely of animal origin. In the efforts of states to prevent transmission and save lives, it is necessary to gather as much information as possible about the origin, spread, and pathogenesis of the disease. Data from China, where the virus originated and the first peak of the epidemic occurred, therefore serves as a fundamental source of information.

(zza)

Source: Wu D., Wu T., Liu Q., Yang Z. The SARS-CoV-2 outbreak: what we know. Int J Infect Dis 2020 Mar 11, pii: S1201-9712(20)30123-5, doi: 10.1016/j.ijid.2020.03.004 [Epub ahead of print].