Contact lenses, trauma top microbial keratitis risks in hospital patients

Patients were evaluated to identify predisposing factors, treatment costs and visual outcome. Treatment requires significant hospital resources, study says.

ByKatrina Altersitz

Contact lens wear and ocular trauma were the most common predisposing risk factors associated with a diagnosis of microbial keratitis in hospital patients ranging in age from 15 to 64, according to a recent study.

Treatment of these cases required significant hospital resources and the keratitis occasionally resulted in vision loss, according to Lisa Keay, BOptom, and colleagues from Australia. The vision loss, along with the cost of treatment, was directly related to the pathogen involved, and not to the risk factors, the study found.

The researchers studied a relatively young population – no one was older than 64 – in order to rule out other predisposing factors associated with aging.

“Defining the predisposing factors, visual outcome and associated costs is important for understanding the impact of microbial keratitis on young adults,” the investigators said. “By examining a younger group, we were more likely to isolate the effects of microbial keratitis uncomplicated by other systemic and ocular disease states.”

Predisposition

The study included 291 cases of microbial keratitis, as well as cases that received treatment consistent with microbial keratitis. These cases were reviewed to identify predisposing factors that led to the conditions.

The researchers noted that in previous studies involving older patients with eye disease or previous ocular surgery, “the most commonly associated factors [for microbial keratitis] were ocular surgery and glaucoma, rare in 15- to 64-year-olds,” they said. Those factors presented less frequently in this study, they added.

Ocular trauma accounted for 36% of the microbial keratitis cases in this study, likely because the population was still of working age, the study found. The trauma was frequently due to welding or grinding, and 90.6% of the injured patients were men.

Contact lens wear was the second most common predisposition, affecting 34% of the study population. Researchers said it was more common among younger patients, a fact supported by earlier studies. The mean age for contact lens-related microbial keratitis was 33 years old, the same as the average age of contact lens wearers in Australia.

Gram-negative organisms were detected more often isolated in contact lens wearers than in trauma patients. Small percentages of the patient group had microbial keratitis associated with other factors, such as ocular surface disease, herpetic eye disease, systemic conditions or a combination of these factors.

Treatment and cost

The study found that the most common treatment regimen used was ciprofloxacin, which was administered to 80% of the patients. This finding contradicted an earlier study from 1999 and 2000 in Auckland where only 28% of the patients received ciprofloxacin while 64% were treated with a combination of tobramycin and cephazolin.

Medication made up less than 10% of the estimated cost to patients treated for microbial keratitis. The investigators did not calculate the cost for each individual patient, but rather estimated based on the components of treatment, including outpatient visits, hospital bed days and medications.

“The largest component of costs was hospital visits and hospital bed days,” the researchers said.

They estimated that treatment cost less than $1,000 in 86% of contact lens-related cases and in 76% of ocular trauma-related cases. Cost within other groups varied and was highest for herpetic keratitis patients, 50% of whom spent more than $1,000.

Acanthamoeba and fungal keratitis were the most expensive isolates to treat, while herpetic keratitis and gram-negative infections fell in between.

The investigators warned that these costs could be irrelevant in other centers because of varying criteria for hospital admittance.

“Although there may be inaccuracies in this estimate of cost, the relative costs and comparisons between groups of patients should be meaningful and are of value,” they said.

They added that prospective studies should also look at the indirect costs not taken into account in this review, including income, inability to drive and need for assistance.

Loss of vision

The researchers said they were limited in measuring vision loss by not knowing the visual acuity of the patients before they were admitted.

The study found that severe vision loss or removal of the affected eye was rare, with only 2.2% of patients falling into that category. Twenty-two percent of patients did have moderate vision loss.

“Visual acuity was reduced in the affected eye relative to the fellow eye by an average of 2.3 lines,” the study said. “However, there was great variability between patients in the amount of visual loss observed.”

The fact that they studied younger patients eliminated considerations of asymmetric cataracts or age-related retinal changes that would affect vision, they said.

The researchers said that, for the first time, they were able to quantify the comparative morbidity of microbial keratitis in terms of visual loss and costs of treatment.

“This study has shown that microbial keratitis can have significant morbidity in terms of both direct costs and visual outcome,” they said.

For Your Information:

Lisa Keay, BOptom, can be reached at Level 3, North Wing, Rupert Myers Building, Gate 14, Barker Street, University of NSW, NSW 2052, Australia.

Reference:

Keay, L, Edwards, K, et al. Microbial keratitis predisposing factors and morbidity. Ophthalmology. 2006;113:109-116.

Katrina Altersitz is an OSN Staff Writer who covers all aspects of ophthalmology.