Microbial keratitis may have a relatively high incidence rate in patients with a history of contact lens use, coexistent autoimmune disease, infiltrates with indistinct edges, and ring infiltrates, according to findings published in Eye & Contact Lens.

The study included a microbial infection group and a polymicrobial infection group. Researchers analyzed demographic and clinical characteristics, risk factors, Gram stains, cultures, and antibiotic sensitivity. Of the 656 study participants, researchers found more than one microorganism in 31.5%. Polymicrobial keratitis (PMK) was identified in 46.5% (n=336) of 723 gram-positive bacteria that were isolated, and also in 61.5% (n=99) of 161 gram-negative bacteria.

The study also found that 0.6% (n=14) patients presented ring infiltrate, and 71.4% (n=10) of those patients had PMK (P =.001). Via multivariate analysis, the researchers concluded that patients had a larger risk of polymicrobial infection when they had a history of contact lens use (P =.042), coexistent autoimmune disease (P =.03), irregular edges of the infiltrate (P =.005), and ring infiltrate (P =.005). Finally, a high sensitivity to Netilmicin was identified in patients in the PMK group. 

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The researchers note that the significantly higher incidence of PMK found in the present study could be due to factors such as the low number of patients studied in previous reports, as well as the higher frequency of bacterial keratitis in North America, as compared with other countries with higher incidence rates of fungal keratitis. 

The study explains that, since ring-shaped infiltrates are rare in fungal keratitis, previous PMK studies may not have reported their presence.

“The cases with ring-shaped infiltrate reported in the literature include acanthamoeba infection, gram-negative organisms, and herpes, and also in animal models after systemic immunizations ring infiltrates have been reported,” the research notes.

Study limitations include its retrospective nature and its participant base, which consisted of patients of an academic tertiary referral center; for this reason, researchers say the study may not reflect the causative agents and sensitivity of infections of the general population. 

Disclosure: Several study authors declared affiliations with the biotech or pharmaceutical industries. Please see the original reference for a full list of authors’ disclosures.


González-Dibildox LA, Oyervidez-Alvarad JA, Vazquez-Romo KA. Polymicrobial keratitis: risk factors, clinical characteristics, bacterial profile, and antimicrobial resistance. Eye Contact Lens. February 18, 2021. doi:10.1097/ICL.0000000000000777