Clinical diagnostic criteria for isolating patients admitted to hospital with suspected pandemic influenza

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Australian hospitals have now experienced the fi rst wave of pandemic H1N1 infl uenza during a southern hemisphere winter. Patients admitted to Australian hospitals with suspected pandemic infl uenza during this period were identifi ed by use of approved national clinical diagnostic criteria. However, the imprecise nature of clinical diagnosis limited the ability of hospitals to isolate infectious patients eff ectively before the laboratory confi rmation of infection (which typically takes a minimum of 48 h). Concern about our reliance on these criteria to isolate potentially infectious patients led us to analyse our early experience with pandemic infl uenza at the two teaching hospitals in the Gold Coast region of Queensland. We collected nasopharyngeal and throat specimens and reviewed clinical and laboratory data on all 346 patients admitted to the hospitals with acute respiratory disease during the period from May 24 to Aug 16, 2009. Pandemic H1N1 infl uenza virus RNA was detected in specimens collected from 106 of 346 patients (31%). On the basis of our experience, we compared the performance of Australian clinical diagnostic criteria with those of WHO, the US Centers for Disease Control and Prevention (CDC), and the UK Health Protection Agency (HPA; table). We make the following observations: (1) Criteria that rely on documented fever (eg, those of WHO and CDC) sacrifi ce sensitivity for specifi city. In our recent experience, 41 of 106 admitted patients (39%) with laboratory-confi rmed pandemic infl uenza did not have any tempera ture recorded above 37·8°C at any stage during their admission. Such criteria are simply not sensitive enough to support good hospital infection control practice. (2) Criteria that include a “history” of fever and respiratory symptoms rather than a documented fever (eg, those of the HPA and the Australian Government Department of Health and Ageing) are adequately sensitive to the diagnosis of pandemic infl uenza. However, the resulting lack of specifi city overwhelmed the ability of our hospitals to isolate suspected cases and resulted in cohorting of infected cases with wrongly suspected cases. (3) Age seems to be a useful criterion by which to discriminate pandemic infl uenza (H1N1) from other causes of acute respiratory disease necessitating hospital admission. Only four of 106 patients admitted with the infection were older than 65 years in our population. 80 (33%) of 240 patients admitted with acute respiratory disease not due to pandemic infl uenza were older than 65 years. Given the limitations of existing criteria, we have adopted a modifi ed approach with better sensitivity and specifi city for the purpose of isolating patients admitted to hospital during the pandemic: age less than 65 years and history suggestive of fever and cough or sore throat.