Early experience of the pandemic influenza H1N1 2009 epidemic in Taiwan

Background: A novel influenza H1N1 began in March 2009, rapidly spread, and then became a pandemic outbreak. Diagnosis by polymerase chain reaction result was not always available because of a surge in workload and therefore clinical diagnosis became important. However, clinical differences between the patients infected by the novel H1N1 virus and those infected by the influenza-like non-novel H1N1 have not been reported. This study was conducted to compare the demographic background, clinical manifestations, and laboratory findings between novel H1N1 influenza infections and other non-novel H1N1 infections.
Methods: At an early stage of H1N1 spread, cases presenting with influenza-like symptom and travel or contact history were quarantined into infection disease-designated hospitals in Taiwan. Data on consecutive patients under investigation for infection with novel influenza A (H1N1) were collected between April 29 and June 19, 2009. The data set consisted of clinical manifestations, plain chest radiography, hematological results, and biochemical findings. Testing of nasopharyngeal swab samples by reverse transcription polymerase chain reaction was used to detect H1N1.
Results: Overall, 166 cases were collected. Among these individuals, there were 14 confirmed H1N1 cases. The clinical manifestations of the H1N1 cases included fever in 13 patients (92.9%), followed by cough, rhinorrhea, a sore throat, myalgia, headache, malaise, abdominal tenderness, and diarrhea. Leukopenia was present in nine patients (64.2%) and lymphocytopenia was present in five (35.7%). The duration of virus shedding was 7.0 ± 1.8 days. When compared with the non-H1N1 cases by multiple logistic regression analysis, cases infected by the novel H1N1 virus were more likely to be younger than 20 years [Odds ratio (OR) = 27.7, 95% confidence interval (CI) = 1.3-597.8, p = 0.034), have traveled from the US (OR = 14.5, 95% CI = 2.1-101.4, p = 0.007) or Thailand (OR = 56.7, 95% CI = 4.6-700.6, p = 0.002) and to have presented with myalgia (OR = 8.5, 95% CI = 1.4-52.0, p = 0.021) or leukopenia (OR = 17.4, 95% CI = 3.4-90.5, p = 0.001).
Conclusion: When a patient presents with influenza-like acute febrile respiratory illness symptoms and is young in age, has a travel history involving an affected area, and is suffering from myalgia or leukopenia, physicians should be alerted to the possibility of novel H1N1 virus infection.