Human infection with avian influenza A H7N9 virus: an assessment of clinical severity
Summary
Background
Characterisation of the severity profile of human infections
with influenza viruses of animal origin is a part of pandemic risk assessment,
and an important part of the assessment of disease epidemiology. Our objective
was to assess the clinical severity of human infections with avian influenza A
H7N9 virus, which emerged in China
in early 2013.
Methods
We obtained information about laboratory-confirmed cases of
avian influenza A H7N9 virus infection reported as of May 28, 2013, from an
integrated database built by the Chinese
Center for Disease
Control and Prevention. We estimated the risk of fatality, mechanical
ventilation, and admission to the intensive care unit for patients who required
hospital admission for medical reasons. We also used information about
laboratory-confirmed cases detected through sentinel influenza-like illness
surveillance to estimate the symptomatic case fatality risk.
Findings
Of 123 patients with laboratory-confirmed avian influenza A
H7N9 virus infection who were admitted to hospital, 37 (30%) had died and 69
(56%) had recovered by May 28, 2013. After we accounted for incomplete data for
17 patients who were still in hospital, we estimated the fatality risk for all
ages to be 36% (95% CI 26—45) on admission to hospital. Risks of mechanical
ventilation or fatality (69%, 95% CI 60—77) and of admission to an intensive
care unit, mechanical ventilation, or fatality (83%, 76—90) were high. With
assumptions about coverage of the sentinel surveillance network and
health-care-seeking behaviour for patients with influenza-like illness
associated with influenza A H7N9 virus infection, and pro-rata extrapolation,
we estimated that the symptomatic case fatality risk could be between 160
(63—460) and 2800 (1000—9400) per 100 000 symptomatic cases.
Interpretation
Human infections with avian influenza A H7N9 virus seem to be less serious than has been previously reported. Many mild cases might already have occurred. Continued vigilance and sustained intensive control efforts are needed to minimise the risk of humanThis article available The Lancet Journal 2013. Further details Contact: Librarian. VMMC
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