Clinical factors predictive of PCR positive in pandemic H1N1 2009 influenza virus infection

OBJECTIVE Pandemic H1N1 2009 influenza virus (H1N1) has been spreading globally. Clinical features might be predictive and may be different among countries. Even though the PCR test is a confirmatory test for this viral infection, it is expensive and limited in most Thai health care facilities. We studied predictive factors of PCR positive in H1N1 suspected patients. METHODS Consecutive patients who had influenza-like illness less than seven days and had been tested for H1N1 by the real-time PCR method between May and July 2009 were enrolled. Clinical data was collected and compared between those who had positive and negative PCR tests. RESULTS There were 6494 patients had flu-like symptoms. Of those, 166 patients were done PCR test and 75 patients (45·18%) had positive PCR test. There were four predictors for positive PCR test including history of contact with confirmed H1N1 patients, headache, body temperature, and coryza with the adjusted odds ratio (95% confidence interval) of 2·84 (1·09-7·40), 6·25 (1·42-27·49), 1·69 (1·08-2·66), and 0·31 (0·12-0·79), respectively. CONCLUSIONS Clinical factors can be both suggestive and protective factors for H1N1 infection. These factors may be helpful in clinical practice to assess the possibility of the H1N1 infection in people who are at risk; particularly in resource-limited health care facilities.