A recent study published in the British Journal of Ophthalmology provided an epidemiological update on bacterial keratitis (BK), including leading risk factors and changes to bacteria distribution.
Give me some background.
BK is the most common form of infectious keratitis and it is treated with intensive broad-spectrum topical antibiotics.
However, the proliferation of antimicrobial resistance (AMR)—particularly in the US and Asia—has caused numerous obstacles to treating BK.
Anything else?
Of note, a previous epidemiological BK study was conducted in the same tertiary care center (the French National Vision Hospital, Paris, France) as this study between 1998 and 1999.
As such, researchers sought to elucidate the potential changes in BK risk factors, clinical presentations, prognosis, and microbiological epidemiology.
Now the study.
In this retrospective study, investigators analyzed the records of 354 patients with BK (documented with microbiological corneal scraping or resolution with antibiotics treatment) in a tertiary ophthalmology center over 20 months (January 2020-September 2021).
The research team sought to compare these results to the previous study from 20 years ago.
Findings?
In 95.2% of patients in the study, one or several of the risk factors listed below were identified:
- Contact lens wear: 45.2%
- Ocular surface disease (OSD): 25.0%
- Systemic disease: 21.8%
- Ocular trauma: 11.9%
- Ocular surgery: 8.8%
Additionally, the positivity rate of corneal scrapings was 82.5%, with 18.2% being polybacterial.
What about the distribution of bacteria?
Of note, 175 (59.9%) of bacteria were Gram-negative, and 117 (40.1%) were Gram-positive.
Further, Gram-negative bacteria were responsible for deeper and more extensive infiltrates in younger patients (p= 0.003).
The most commonly found bacteria were:
- Pseudomonas (P.) aeruginosa: 32.5%
- Moraxella spp: 18.1%
- Staphylococcus (S.) aureus: 8.2%
Talk about visual acuity.
Final visual acuity (LogMar) was associated with:
- Age (p=0.0001)
- Infiltrate size (p<0.0001)
- OSD (p=0.03)
- Ocular trauma (p=0.02)
- Contact lens wear (p<0.0001)
Compare the findings from this study to the previous one.
The positivity rate of corneal scrapings and the proportion of Gram-negative bacteria—particularly Moraxella spp—increased.
In addition, all P. aeruginosa and Moraxella spp were sensitive to quinolones, and all S. aureus were sensitive to both quinolones and methicillin.
Expert opinion?
The study authors noted that they found no methicillin-resistant S. aureus (MRSA) during the study period.
They theorized that this could be explained by “the systematic use of three fortified topical antibiotics (i.e., piperacillin [20 mg/mL], gentamicin [15 mg/mL], and vancomycin [50 mg/mL]) for severe keratitis and the frequent use of topical quinolones in combination with another antibiotic.”
Take home.
These findings suggest that contact lens wear remains a leading risk factor for BK—highlighting the importance for eyecare practitioners to teach patients about contact lens hygiene.
Further, the bacteria distribution has shifted, with a majority of Gram-negative bacteria and an increased presence of Moraxella spp.
Lastly, the study found an increase in the positivity rate of corneal scrapings.