A Rise in Acanthamoeba Eye Infections in Iowa, 2002–2017 — and Contact Lens Habits

Acanthamoeba is a microscopic organism found almost everywhere, feeding on bacteria and yeast. It can form hardy cysts that survive extreme conditions, which makes it hard to kill. In the eye it causes Acanthamoeba keratitis (AK), a severe infection of the cornea that can lead to painful blindness. Contact lens wearers exposed to any water are at highest risk. AK is often underdiagnosed, because what patients show when they seek care varies, and it is difficult for eye doctors to treat.

More cases than expected

In the United States, AK strikes an estimated one to two new cases per 1 million contact lens wearers a year, and approximately 16.7% of adults wear contact lenses. Among Iowa’s estimated 2.42 million adults — 404,267 of them expected to wear lenses — that predicts 0.4–0.8 new cases a year.

Yet in 2015 alone, University of Iowa Hospitals & Clinics (UIHC), the state’s only tertiary care center, diagnosed 15 new cases, 14 of them in adults. So researchers reviewed every corneal infection UIHC treated from 2002 to 2017.

What they found

They confirmed 111 AK cases, 75 (67.6%) in Iowa residents. UIHC likely saw nearly all of Iowa’s cases: AK can’t be diagnosed without testing, and the hospital has the state’s only clinical eye confocal microscope and its only ocular pathologist.

Population growth can’t explain the rise. Iowa’s adult population grew 7.3% over the period, which would add only 0.03–0.06 expected cases. Instead, the average number of new cases among Iowans rose from 2.9 a year in 2002–2009 to 6.5 a year in 2010–2017, and doubled during 2012–2014.

Confirmed Acanthamoeba keratitis cases in Iowa residents treated at UIHC, 2002–2017. Image from CDC’s report.

The patients

Iowans with AK had a median age of 32 (range 8–80); 40 (53.3%) were women and 6 (8%) were under 18. Most had at least one risk factor:

Among the 63 contact lens wearers, 54 (85.7%) reported poor lens hygiene, and most reported recent water exposure:

• swimming in lakes or rivers in their lenses — 14
• showering in their lenses — 11
• cleaning lenses with tap water — 8
• sleeping in their lenses — 21
• wearing them longer than recommended — 19

Cases peaked in summer (23), followed by fall (21), winter (16) and spring (15). Diagnosis took an average of 1.2 months after symptoms began, and the delay cost sight: 31 (41.3%) were legally blind in the affected eye at their first visit, and 35 (46.7%) eventually needed surgery because the organism resisted medicine.

Why the rise?

AK outbreaks elsewhere have been linked to certain contact lens solutions, hard water with lime scale, and biofilm in household and recreational water. The authors suggest that growing algal blooms and nutrient pollution in Iowa’s waters may be helping disease-causing Acanthamoeba thrive. The study looked back at records from one center, though that center likely sees most of Iowa’s cases.

Protecting your eyes

CDC advises contact lens wearers not to:

• clean lenses with tap water
• swim or shower while wearing them
• wear them longer than recommended
• sleep in them

Sources

Based on Scruggs BA, Quist TS, Salinas JL, Greiner MA, "Notes from the Field: Acanthamoeba Keratitis Cases — Iowa, 2002–2017," MMWR Vol. 68, No. 19, CDC; a work of the United States government in the public domain.