An 84-year-old gentleman presented with a 3-day history of fevers, non-productive cough, mild headache and delirium. His previous medical history included hypertension, hypercholesterolemia, atrial fibrillation and hearing impairment. He was living at home in a semi-rural area of New South Wales with his partner and was fully independent in his activities of daily living. He was an ex-smoker having ceased smoking in his thirties. He had worked as a plumber with minor asbestos exposure.
On presentation, he was febrile to 39.6  and his pulse oximetry was 94% on room air with a respiratory rate of 18. Physical examination revealed inspiratory crackles in the left upper zone. He was cardiovascularly stable.
Ten days prior to developing symptoms, the patient was working in his outdoor backyard garden shovelling approximately 500 kg of topsoil and home compost. The patient was also exposed to two 25 kg bags of commercial potting mix that were stored in his garden shed. In the process of preparing and working with soil and compost materials, the patient did not practice strict infection control measures, including wearing of masks, frequent handwashing and opening bags of commercial potting mix in well ventilated areas. The patient also had no recent sick contacts, no overseas travel, no contact with air-conditioning units or cooling towers and no exposure to birds.
His white blood cell count was 14.6 x 109/L (neutrophil count 12.3 x 109/L, lymphocyte count 1.0 x 109/L) and his C-reactive protein level was 210 mg/L. He also suffered from acute on chronic kidney injury with a creatinine level of 131 micromol/L (Table 1). His liver function tests were unremarkable. A chest radiograph showed consolidation in the left upper lobe (Fig. 1). His initial diagnosis was lobar community-acquired pneumonia, and as per local antimicrobial guidelines he was empirically treated with intravenous benzylpenicillin and oral doxycycline.
The patient tested positive for L. pneumophilia 1 antigen in his urine sample with urinary antigen enzyme immunoassay, and his antibiotic regimen was changed to dual therapy with azithromycin 500mg once daily and ciprofloxacin 500mg twice daily for 48 hours, followed by monotherapy with azithromycin 500mg once daily.
Nasopharyngeal swabs for polymerase chain reaction (PCR) testing confirmed L. pneumophilia infection. Both acute and follow-up convalescent serologies were negative for L. pneumophilia and L. longbeachae.
Sampling and analysis of suspected contaminated home soil was not feasible as this was a single isolated case and no home soil was available for sampling. The patient denied having any exposure to ponds, fountains and other sources of stagnant water at home. A notification was made to the local public health unit and because this was an isolated case, no further investigation or contact tracing was necessary as there were no other outbreaks of Legionnaires' disease at the time of presentation. Thorough review of the clinical presentation strongly suggests that there were no other sources that the patient could have acquired the infection except for his recent exposure to home soil and potting mix.