Investigators get to the root of ocular infections

A retrospective study published in the Iran Journal of Public Health examined the microbiological profile of ocular infections, finding the specimens obtained from the cornea as the most common submitted specimens to the microbiology laboratory.

Investigators conducted a cross-sectional investigation where they gathered data of ocular specimens obtained from patients who were investigated for ocular infections at the Farabi Eye Tertiary Referral Hospital, a facility that has a large catchment area as many patients from all regions of Iran, both rural and urban, are referred for investigation.

The specimens had been collected over a 7-year period (2011 to 2018). They reviewed results in a retrospective fashion.

“We aimed to determine the spectrum of responsible bacterial and fungal agents in patients with suspected ocular infections referred to Farabi Eye Tertiary Referral Hospital, Tehran, Iran,” wrote the authors.

The authors of the study explained the importance of identifying micro-organisms as they can be culprits linked to ocular infections.

“If ocular infections are untreated, severe morbidities may arise,” the authors wrote. “Isolation of the offending microorganisms is essential, as patterns vary with geographic location.”

The authors also pointed out appropriate antibiotic management can be determined with accurate identification of microorganisms.

They noted that changes in the ocular surface commensals can cause infections including blepharitis, keratitis, conjunctivitis, canaliculitis, orbital cellulitis, and endophthalmitis.

A total of 16,656 ocular samples were evaluated in this investigation. The mean age of patients was 48.31 years old, and the majority of patients were men (60.33%). Men in their 70s was the largest represented group in the study. Investigators also obtained data such as patient age, sex, hospitalization status at the time the specimen was collected, specimen collection sites, gram stain reports and results of culture.

In terms of methods, heat-fixed smears were prepared on alcohol-cleansed microscope slides for smear and gram staining, with inoculations performed onto various culture media, the authors explained.

The cornea was the most sampled site, with 49.24% of specimens coming from the cornea. It accounted for the largest number of specimens regardless of seasons, with it making up 43.88% of specimens in the winter and 51.83% in the summer. After the cornea, the conjunctiva and vitreous humor were most commonly sampled. Other specimens obtained from aqueous humor, contact lens solution, lacrimal drainage system, lacrimal sac, eyelid ulcer, orbit, foreign body, orbital implant, buckle, and dermoid cyst.

Investigators noted that no documentation was available to support that all patients had presented their contact lens cases for sampling over the entire study period. Of the 8201 cornea specimens, only 600 (7.3%) were accompanied by a sample of contact lens solution.

Of the 16,656 total smears, microorganisms were not seen in the majority (9432 or more than 56.63%) and there were microorganisms seen in the balance of smears (7224). Gram staining of those 7224 microorganisms revealed the vast majority were bacteria (6515), followed by fungi (672), and a very small number (37) contained both bacteria and fungi. “Most positive culture results were bacterial, and only approximately 10% of cases were fungal,” wrote the authors.

Of positive gram staining bacterial specimens, 56.5% demonstrated gram-positive cocci, the authors noted.

Of the total number of smears where microorganisms were seen (7224) and gram stained, most appear to have been from patients who were not hospitalized and were outpatients: 440 of 672 fungi (65.48%), 4,567 of 6,515 bacteria (70.10%), and 32 of 37 where there were both bacteria and fungi (86.49%).

The most isolated bacteria were Pseudomonas aeruginosa (17.77%), Staphylococcus epidermidis (13.80%), Streptococcus pneumoniae (13.27%), S. viridans (12.23%), and S. aureus (11.18%). Among 733 cases with cultures positive for S. aureus, 22 were reported as methicillin-resistant staph aureus. The most isolated fungal microorganisms were Fusarium spp., followed by Aspergillus spp., and Candida albicans.

The authors noted one of the strengths of this investigation is the sample size.

“To our knowledge, this is the largest study on the bacterial and fungal profiles of ocular infection in the literature,” the authors concluded, pointing out another strength is the extended study duration.

The authors noted that the investigation had numerous limitations. One limitation was that in 43 (5.89%) of the 730 specimens with positive fungal culture, the exact type of fungi was not mentioned.

They noted a major limitation was the failure to measure the incidence of ocular infections. Moreover, they were unable to pinpoint the associated risk factors for ocular infections. The lack of data on clinical diagnosis, antibiotic susceptibility, and concomitant medical reports of cases were other potential limitations of this study that the authors identified.

The authors recommended that future studies incorporate clinical examinations and predisposing factors such as occupational exposure, history of trauma, or contact lens wear, while considering comorbidities and clinical outcomes.