Initial observations showed a pyrexia of 40.2, Sp02 93% on room air, respiratory rate 25/min, heart rate 170 bpm, blood pressure 110/70 mm Hg. Bibasal crepitations were present on chest auscultation with dullness to percussion at the right base. An ECG confirmed atrial flutter with a rapid ventricular response. The chest x-ray showed widespread pulmonary infiltrates (figure 1).

The patient was given a stat dose of metoprolol intravenously and subsequently reverted to sinus rhythm. Oral beta blocker was maintained thereafter.

Swine flu was diagnosed on the basis of symptoms and a positive RIDT. Initial treatment was with oseltamivir 75 mg twice daily and the patient moved to an isolated side room as per hospital infection policy.

These symptoms are obviously not specific to influenza. Current recommendations advise that further confirmatory testing in the community is unnecessary unless hospital admission is required.⁵ Beyond clinical diagnosis, RT-PCR is the gold standard laboratory test for confirmation of influenza A, but this has a turnaround time of 48–96 hours.^{6 7}

For early diagnosis and appropriate isolation of suspected cases in patients admitted to hospital, rapid influenza antigen testing is now available and recommended by WHO.⁸

In our institution, potential swine flu cases are immediately swabbed using the Remmel X-pect Flu A&B (REMEL Inc, Lenexa, KS, USA) rapid testing kit.^9–11 This result is available in 15 min and positive results are sent for confirmation using PCR. To date, studies have suggested a very high sensitivity (78–97.8%) and specificity (95–100%).^9–11 However, in this patient's case, the result proved to be a false-positive. We believe this case describes one of the first reports of a false-positive result with this assay. At the time of submission we are aware of an isolated case of Legionella pneumonia misdiagnosed as swine flu publicised on the internet but not yet as a case report. Other reports describe misdiagnosis of meningitis during an influenza pandemic and the role of decision support algorithms.^12–14 These cases have all been in the community and in patients who have been diagnosed on a clinical basis without recourse to laboratory or point of care rapid testing. We are unaware of any report describing a positive rapid care test for swine flu with a subsequent negative real-time PCR test that has manifested Legionella pneumonia.

Both morbidity and mortality in Legionella infection are adversely affected by delayed treatment.³ We believe that this patient's initial misdiagnosis as a case of H1N1 influenza A was largely due to the protean nature of the presenting symptoms and a positive rapid swab test ( in keeping with current guidelines.) Therefore, commencement of appropriate antibiotic treatment was delayed, although fortunately in this instance the patient made a full recovery. We feel that this case emphasises the need for vigilance during the influenza pandemic.