An evaluation of diagnostic tests in a case series of suspected leptospirosis patients seen in primary care.

AIMS This study describes 47 presentations of suspected leptospirosis in general practice in New Zealand. Our primary aim was to assess the laboratory diagnosis of leptospirosis in these patients, by comparing polymerase chain reaction (PCR) tests, microscopic agglutination test (MAT) and culture results. METHODS Patients suspected of leptospirosis were recruited from general practices in the Waikato (n=17) and Wairoa (n=30) between August 2011 and June 2015. Blood and urine samples were tested for leptospirosis at two diagnostic laboratories and one research laboratory using PCR tests, MAT and culture. RESULTS Forty-seven patients were recruited for this study: 37 during the acute phase of the illness (within 10 days of symptom onset) and 10 after the acute phase. Eleven of the acute phase patients (11/37, 30%) and two of the later phase patients (2/10, 20%) returned positive leptospirosis test results. The 11 acute phase leptospirosis positive patients had the following positive diagnostic tests: PCR and paired MAT (+/- blood culture) (n=3), PCR only (+/- blood culture) (n=4), paired MAT only (n=3) and blood culture only (n=1). Urine PCR (performed only on Wairoa patients) was the only positive test for two of these patients. CONCLUSION About a quarter of farm workers and meat workers presenting to general practice with flu-like symptoms will have leptospirosis, but they will not be diagnosed unless appropriately tested, and then they may only test positive for some of the tests available. To increase the likelihood of making a diagnosis, clinicians should order multiple laboratory tests, including blood and urine PCR and a paired MAT.