Analysis of the risk factors for influenza A (H1N1) pneumonia

Pneumonia is the most common complication of influenza A (H1N1). However, there has been no identification of any single initial symptom as an independent risk factor. In 2009, 206 patients were diagnosed with H1N1 in the Chengde area, China and they were assembled in the Chengde Hospital for Infectious Diseases. The diagnosis and treatment were performed in accordance with the Protocol for Diagnosis and Treatment of Influenza A (H1N1) (2009, third edition), issued by the General Office of the Ministry of Health, with detailed records by the medical staff assigned by the Bureau of Health of the Chengde government. All the patients had viral nucleic acid-positive throat swabs detected with quantitative reverse transcription polymerase chain reaction (qPCR). Based on the final imaging findings, patients were divided into the pneumonia and non-pneumonia groups for this case control study. The univariate analysis demonstrated that the ratios of patients aged 0-5 and ≥45 years, with underlying diseases, with initial symptoms including cough, expectoration and dyspnea and with onset-to-treatment interval of >48 h were higher in the pneumonia compared to the non-pneumonia group (P<0.001, P<0.001, P=0.018, P<0.001, P<0.001 and P<0.001, respectively). The multivariate logistic regression analysis demonstrated that age 0-5 years, presence of underlying diseases, expectoration as the initial symptom and onset-to-treatment interval of >48 h were the independent risk factors for pneumonia with relative odds ratios (OR) and 95% confidence intervals (95% CIs) of 6.120 and 1.779-21.088, 11.188 and 2.021-61.935, 5.263 and 2.042-13.562, and 22.873 and 6.110-85.631, respectively (P<0.01). Therefore, it is recommended that patients with H1N1 presenting with expectoration as the initial symptom be treated with caution during influenza pandemics.