Nontuberculous mycobacteria-associated infections on the rise

This retrospective study of ocular infections caused by nontuberculous mycobacteria (NTM) seen at a tertiary referral center found that the incidence has increased within the last eight years, with a high number of biomaterial associated infections occurring. The authors say their results confirm that clinical diagnosis and microbiological confirmation of these infections remains challenging, with the preferred antibiotic treatment unclear. However, they conclude that outcomes may be improved by early diagnosis and appropriate therapy.

The study included 139 patients with culture-confirmed NTM infections seen from January 1980 through July 2007. A chart review identified 183 NTM isolates from 142 eyes, with a four-fold increase in the number of eyes infected with NTM from 1980 to 1989 (13.4 percent) compared with 2000 to 2007 (56.3 percent).

NTM isolates from the M. abscessus/chelonae complex were the most frequently recovered (83 percent) and difficult-to-manage pathogens. Ninety-one percent of isolates were recovered within 10 days.

Common diagnoses included keratitis (36.6 percent), scleral buckle infections (14.8 percent) and socket/implant infections (14.8 percent). Risk factors included the presence of biomaterials (63.1 percent), ocular surgery (24.1 percent) and steroid exposure (77 percent).

The median time from diagnosis of culture positive NTM infection to resolution was 13 to 24 weeks. Combination therapy was used to treat 80 percent of infected eyes. Eighty-one percent of nontuberculous mycobacteria isolates were susceptible to amikacin, ninety-three percent to clarithromycin and 21 percent to moxifloxacin.

Based on this study and emerging trends, the authors predict an increase in the incidence of NTM ocular infections. They say major factors that will likely contribute to this increase are the rising use of biomaterials, increasing number of ocular surgeries (LASIK, endothelial keratoplasty) and expanded use of fluoroquinolones for prophylaxis (intravitreal injections, refractive surgeries). Strategies for reducing the incidence and pathology of NTM infections include proper sterilization of instruments and intraoperative sterile techniques, disinfection of skin and eyelids with povidone-iodine, and use of pre- and postoperative prophylactic antibiotics.

The authors recommend that both smears and cultures be collected immediately for evaluation in patients with clinical signs and symptoms suggestive of NTM infection.