Evolution Of Incidence, Microbiological Profile And Antibiotic Resistance In Bacterial Keratitis Before, During And After The Covid-19 Pandemic In A Tertiary Referral Centre

To evaluate changes in incidence, microbiological profile and antimicrobial resistance patterns

of bacterial keratitis across three periods: pre-COVID (2018–2019), COVID (2020–2021) and

post-COVID (2022–2024). We hypothesized that the pandemic and associated clinical changes

significantly modified both microbial distribution and antimicrobial resistance patterns in the

general population.

Retrospective study conducted at Hospital General Universitario Gregorio Marañón, a tertiary

referral centre in Madrid, Spain.

Methods: Observational, retrospective study of patients with suspected infectious corneal ulcer

and corneal scraping between 2018–2024. Only microbiologically confirmed bacterial keratitis

cases with available antibiogram were included. Patients were divided into: pre-COVID (n=41),

COVID (n=32) and post-COVID (n=51). Microorganism identification and susceptibility were

performed according to CLSI/EUCAST criteria. Categorical variables were expressed as

frequencies and percentages. Comparisons used chi-square or Fisher’s exact test. P<0.05 was

significant. Contact lens wear was recorded.

A total of 124 patients were included. A significant shift in microbiological profile was observed

across periods. Gram-positive bacteria predominated in pre-COVID (87.8%) and COVID

(81.2%) periods, but decreased to 54.9% post-COVID. Conversely, Gram-negative bacilli

showed a significant increase in the post-COVID period (45.1% vs 12.2% pre-COVID;

p=0.00079).

Pseudomonas aeruginosa emerged as the most frequent pathogen post-COVID (37.2%),

compared to pre-pandemic dominance of Staphylococcus spp. and Streptococcus pneumoniae.

A significant increase in resistance to fluoroquinolones (Ciprofloxacin) was observed in the

post-COVID period compared with pre-COVID (19.6% vs 7.3%, p<0.05).

In this tertiary-centre cohort, the COVID-19 pandemic was associated with a significant shift in

the microbiological distribution of bacterial keratitis, characterized by a critical increase in

Gram-negative bacilli, particularly Pseudomonas aeruginosa. Furthermore, a significant

increase in resistance to fluoroquinolones was observed in the post-COVID period.

These findings suggest a relevant change in the epidemiology of corneal infections, therefore

the need for continuous microbiological surveillance and reassessment of empirical therapy

protocols in the post-pandemic era.