Abstract
Hospitalization with H7N9 virus infection is associated with older age and chronic heart
disease, and patients have a longer duration of hospitalization than patients with H5N1 or
pH1N1. This suggests that host factors are an important contributor to H7N9 severity.
Background. Influenza A(H7N9) viruses isolated from
humans show features suggesting partial adaptation to mammals. To provide insights into
the pathogenesis of H7N9 virus infection, we compared risk factors, clinical presentation,
and progression of patients hospitalized with H7N9, H5N1, and 2009 pandemic H1N1 (pH1N1)
virus infections.
Methods. We compared individual-level data from
patients hospitalized with infection by H7N9 (n = 123), H5N1 (n = 119; 43
China, 76 Vietnam), and pH1N1 (n = 3486) viruses. We assessed risk factors for
hospitalization after adjustment for age- and sex-specific prevalence of risk factors in
the general Chinese population.
Results. The median age of patients with H7N9 virus
infection was older than other patient groups (63 years; P < .001) and
a higher proportion was male (71%; P < .02). After adjustment
for age and sex, chronic heart disease was associated with an increased risk of
hospitalization with H7N9 (relative risk, 9.68; 95% confidence interval,
5.24–17.9). H7N9 patients had similar patterns of leukopenia, thrombocytopenia, and
elevated alanine aminotransferase, creatinine kinase, C-reactive protein, and lactate
dehydrogenase to those seen in H5N1 patients, which were all significantly different from
pH1N1 patients (P < .005). H7N9 patients had a longer duration of
hospitalization than either H5N1 or pH1N1 patients (P < .001), and the
median time from onset to death was 18 days for H7N9 (P = .002) vs
11 days for H5N1 and 15 days for pH1N1 (P = .154).
Conclusions. The identification of known risk factors
for severe seasonal influenza and the more protracted clinical course compared with that
of H5N1 suggests that host factors are an important contributor to H7N9 severity.
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