The significance of different sample types in study of pandemic A (H1N1) influenza diagnosis

OBJECTIVE: To explore the value of different types of samples, including throat swabs, stools, bloods in pandemic A (H1N1) influenza diagnosis and virus shedding patterns. METHODS: From May to June in 2009, 135 samples were collected from 23 confirmed cases of pandemic influenza A (H1N1) infection, including 99 throat swabs, 14 stools, 11 bloods, 1 respiratory tract washing from 13 confirmed cases and 10 blood samples from other confirmed cases. The virus was detected by real-time RT-PCR, the antibody was detected by haemagglutination inhibition assay. RESULTS: For 99 throat swabs of 13 patients, the median time of the first positive real-time RT-PCR was 1 day (ranged from 0 to 7 days) after the onset of the symptoms of illness; the median length of time duration of positive real-time RT-PCR results from throat swabs was 3 days (ranged from 1 to 15 days). Four cases intermittently released virus. One respiratory tract washing sample was positive. In 14 stools, 8 stools were real-time RT-PCR positive, the positive rate was 57.14%. The median time of the positive real-time RT-PCR was 3 days (ranged from 1 to 4 days) after the onset of the symptoms of illness. In 21 blood samples collected at 2 to 9 days of onset, 1 blood sample was real-time RT-PCR positive, the positive rate was 4.76%. All these 21 blood samples were antibody negative. CONCLUSION: Throat swabs and stools samples can be used as A (H1N1) influenza early diagnosis. The length of time duration of positive real-time RT-PCR in throat swabs was longer than stool samples and intermittently releasing of virus were found in throat swabs. Influenza A H1N1 cases showed the presence of small amount of viremia and antibody was negative in early blood samples (< 9 days).