Epidemiology

The World Health Organization (WHO) was informed of 44 cases of pneumonia of unknown microbial aetiology associated with Wuhan City, Hubei Province, China on 31 December 2019. Most of the patients in the outbreak reported a link to a large seafood and live animal market (Huanan South China Seafood Market).[6] The WHO announced that a novel coronavirus had been detected in samples taken from these patients. Laboratory tests ruled out severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome (MERS)-CoV, influenza, avian influenza, and other common respiratory pathogens.[7] Since then, the outbreak has escalated rapidly, with the WHO first declaring a public health emergency of international concern on 30 January 2020 and then formally declaring it a pandemic on 11 March 2020.

Consult the resources below for updated information on daily case counts:

Data from the largest case series in China to date (72,314 cases from 31 December 2019 to 11 February 2020) found that the majority of confirmed cases (87%) were aged 30 to 79 years, 1% were aged 9 years or younger, 1% were aged 10 to 19 years, and 3% were aged 80 years or older. Approximately 51% of patients were male and 49% were female. Nearly 4% of cases were in healthcare workers.[9]

In the US, older patients (aged ≥65 years) accounted for 31% of all cases, 45% of hospitalisations, 53% of intensive care unit admissions, and 80% of deaths, with the highest incidence of severe outcomes in patients aged ≥85 years.[10]

Infection in children is being reported much less commonly than among adults. A systematic review found that children accounted for 1% to 5% of confirmed cases (depending on the country) so far.[11] All cases so far have been in family clusters or in children who have a history of close contact with an infected patient.[12][13][14] In a case series of 2143 paediatric patients in China, the median age of children was 7 years, and 56.6% of cases were in boys although this gender difference was not considered significant.[15]

Emerging evidence suggests that cold and dry conditions may facilitate the spread of COVID-19; however, further research is required on how weather conditions influence transmission.[16]

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