Infectious Keratitis in Mexico: 10 year experience in corneal scrapes

Abstract

Purpose: To report the distribution, microbiologic trends and antibiotic sensitivity patterns of the infectious keratitis in a ten year period in Mexico City.

Methods: Retrospective study, samples were obtained from corneas with diagnosis of infectious keratitis in the period January 2002 - December 2011. Results of cultures, stains and antibiograms were analyzed.

Results: A total of 1638 consecutive corneal scrapings were taken during the 10 years of the study. A pathogen was recovered in 616 samples (38%), with bacterial keratitis accounting for 544 of the positive cultures (88%). The total number of Gram positives and Gram negatives were 412 and 132, respectively. We detected a non significant increasing trend in Gram negative isolates (P=0.11). The most common isolated pathogen was Staphylococcus epidermidis and the most common Gram-negative bacteria was Pseudomonas aeruginosa. Methicillin resistant Staphylococcus aureus (MRSA) was present in 45.2% of the S aureus isolates; meanwhile 53.7% coagulase-negative Staphylococcus isolates were Methicillin resistant (MRCNS). There was a trend toward increasing in vitro resistance to methicillin from 20.8% in the first 5 years of the study to 79.2% for the last five 5 years (P=0.35). P aeruginosa resistance to ceftazidime increased from 11.1% in the first 5 year period to 88.9% for the last five years of the study (P=0.01). The overall sensitivity for vancomycin of MRSA was 87.5%, while 99.6% of the MRCNS where sensitive. The overall sensitivity of bacterial isolates for ciprofloxacin was 86.7%.

Conclusions: There was a non-significant increase in the recovered Gram positive and Gram negative microorganisms over time. We observed an increased resistance to methicillin in almost a half of the MRSA and MRCNS isolates. Ceftazidime resistant P aeruginosa isolates increased to nearly 90% in the 5 last years of the study, suggesting that this antibiotic is not an ideal empiric treatment. Vancomycin resistant microorganisms accounted for 9.9% of all Gram-positive isolates, while 13.3% of all the bacterial isolates were resistant to quinolones; justifying the latter as monotherapy broad spectrum empirical treatment for bacterial keratitis.

Keywords: 573 keratitis • 479 cornea: clinical science • 422 antibiotics/antifungals/antiparasitics