Enhanced Detection of Legionnaires' Disease by PCR Testing of Induced Sputum and Throat Swabs

To the Editor: Legionnaires’ disease, particularly that caused by non-pneumophila species, is notoriously underdiagnosed [1, 2]. We recently found a four-fold increase in case detection of Legionnaires’ disease through a laboratory-initiated strategy of systematic PCR testing for Legionella species of all lower respiratory specimens from patients with pneumonia or immune compromised status [3]. This strategy relies on the availability of lower respiratory specimens and the recording of relevant clinical information on laboratory requisition forms by clinicians. We recognised that this strategy will miss testing patients who could not expectorate sputum and when inadequate clinical information is written on laboratory requisition forms. To address this diagnostic gap we enhanced case detection by actively identifying patients with community-acquired pneumonia (CAP) and by collecting induced sputum from those unable to expectorate voluntarily. In addition, we evaluated throat swabs as an alternative specimen for PCR testing. From October 2012 to March 2013 patients admitted to Christchurch Hospital and The Princess Margaret Hospital (both in Christchurch, New Zealand) with CAP and aged ≥18 years were recruited. For logistical reasons, recruitment occurred on weekdays only. The study period was chosen to coincide with peak Legionnaires’ disease activity in Christchurch [3]. Patients were excluded if the pneumonia was hospital acquired or associated with bronchial obstruction, bronchiectasis or tuberculosis. Patients were not eligible for sputum induction if they required high-flow oxygen or assisted ventilation at enrolment. Ethical approval was obtained from the New Zealand Northern A Ethics Committee. Informed consent was obtained from the patient or their next of kin with …