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Australian hospitals have now experienced the first wave of pandemic H1N1 influenza during a southern hemisphere winter. Patients admitted to Australian hospitals with suspected pandemic influenza during this period were identified by use of approved national clinical diagnostic criteria.1 However, the imprecise nature of clinical diagnosis limited the ability of hospitals to isolate infectious patients effectively before the laboratory confirmation 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 influenza 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 influenza 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 criteria1 with those of WHO,2 the US Centers for Disease Control and Prevention (CDC),3 and the UK Health Protection Agency4 (HPA; table). We make the following observations:
  • Criteria that rely on documented fever (eg, those of WHO and CDC) sacrifice sensitivity for specificity. In our recent experience, 41 of 106 admitted patients (39%) with laboratory-confirmed pandemic influenza did not have any temperature 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.
  • 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 influenza. However, the resulting lack of specificity overwhelmed the ability of our hospitals to isolate suspected cases and resulted in cohorting of infected cases with wrongly suspected cases.
  • Age seems to be a useful criterion by which to discriminate pandemic influenza (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 influenza were older than 65 years.
Given the limitations of existing criteria, we have adopted a modified approach with better sensitivity and specificity 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.
We declare that we have no conflicts of interest.