Background:

Infectious keratitis is an ophthalmic pathology caused by bacteria and fungi, and rarely by parasites. The success of the treatment depends to a great extent on the early microbiological diagnosis; therefore the role of the laboratory is essential.

Objective:

To evaluate the usefulness of Gram staining compared to culture in the etiological diagnosis of infectious keratitis.

Methodology:

In this study of diagnostic tests, corneal scraping and swab specimens from patients with clinical characteristics of infectious keratitisreferred from three reference centers from Asunción-Paraguay between January 2015 and May 2017 were included. Corneal scraping was used for Gram staining and fungal culture, and the swabs for culture for bacteria.

Results:

Of the 216 samples studied, 75 (34.7%) were positive for culture for fungi and 62 (28.7%) for bacteria. The sensitivity of Gram staining for fungi was 94.7% (71/75), specificity 95.0% (134/141); PPV 91.0% (71/78) and NPV 97.1% (134/138). For bacteria, the sensitivity was 74.2% (46/62), specificity 99.4% (153/154); PPV 97.9% (46/47) and NVP 90.5% (153/169). Fusariumspp was the most frequently isolated fungus (45/75) and among the bacteria Pseudomonas aeruginosa (16/62) and Streptococcus pneumoniae (13/62).

Conclusion:

Gram staining had good diagnostic performance for mycotic keratitis, constituting a simple and quick tool available in any microbiology laboratory. However, the sensitivity for bacteria was relatively low, which may be attributed in some cases to the scarce material and inadequate sample distribution in the smear making observation difficult.

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