Nocardiosis: 7-year experience at an Australian tertiary hospital

Nocardiosis has historically been reported in immunocompromised patients, but Australian epidemiological and antimicrobial susceptibility data are limited.

To describe the epidemiology, diagnosis and initial treatment of nocardiosis in an Australian tertiary hospital over 7 years.

In this retrospective study, all positive cultures for Nocardia species from any site isolated at the Alfred Hospital, Melbourne, between 1 January 2010 and 31 December 2016 were identified, and corresponding laboratory data and medical records reviewed.

Sixty-eight non-duplicate isolates were identified from 67 patients. Common predisposing factors were chronic lung disease (38/67; 57%), organ, particularly lung, transplantation (13/67; 19%) and solid organ malignancy (6/67; 9%); 12% (8/67) of patients had no identifiable systemic risk factors. Seventy-nine percent (53/67) of patients had pulmonary nocardiosis only. Nocardia nova was the most commonly isolated species (20/68; 29%). In 48% (32/67) of patients, Nocardia species were isolated only on specific mycobacterial media. All tested species were susceptible to sulfamethoxazole-trimethoprim and amikacin, with the majority (58/63; 92%) susceptible to imipenem. All-cause mortality rates at 6 and 12 months where data were available were 15% (10/66 patients) and 22% (14/64 patients) respectively.

In the largest Australian series in 25 years, nocardiosis predominantly affected patients with chronic lung disease or impaired cell-mediated immunity. A significant proportion of organisms from pulmonary sites were isolated on mycobacterial culture media only, suggesting that its use may improve yield. Isolates remain highly susceptible to sulfamethoxazole-trimethoprim, amikacin and imipenem, while other agents should be used only after confirmation of in vitro susceptibility.