Nocardiosis in the Tropical Northern Territory of Australia, 1997–2014
Nocardia is an uncommon pathogen, but immunosuppression, its main risk factor, is becoming more frequent. We aimed to evaluate changes in the annual incidence of nocardiosis and in the susceptibility profile of its aetiological agents. Demographic data were analysed for all isolates of Nocardia forwarded to the provincial public health laboratory of Quebec, Canada during the last two decades. Population incidence could be measured from 1997 onwards. Resistance patterns were analysed for those isolates selected for in vitro susceptibility testing. Throughout Quebec, 575 incident cases were identified between 1997 and 2008. The annual incidence of Nocardia infection/colonization increased from 0.33 (1997-1998) to 0.87 (2007-2008) per 100,000 inhabitants (p 0.001). In a small subset of patients for whom detailed clinical information was available, 59% of isolates corresponded to genuine infections. Nocardia farcinica predominated in specimens representing invasive infections (blood, brain, lung or pleural aspirates). Isolates were often non-susceptible to several antimicrobials, with the exception of amikacin and linezolid. Overall, 43% of 157 isolates were non-susceptible to trimethoprim-sulphamethoxazole. In conclusion, Nocardia infection/colonization remains rare. However, from 1997-1998, a progressive increase in incidence was noted in the province of Quebec. In regions such as ours, where a substantial proportion of invasive isolates are non-susceptible in vitro to trimethoprim-sulphamethoxazole, the latter may no longer be the empirical treatment of choice in immunosuppressed and severely ill patients with nocardiosis.