Acanthamoeba keratitis shows similarly low incidence across continents
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Key takeaways:
- The researchers reported a median of 1.9 new cases of Acanthamoeba keratitis per health care center per year.
- No significant difference was found in Acanthamoeba keratitis incidence across continents.
Acanthamoeba keratitis appeared to be a relatively rare disorder with similar incidence around the world, according to a study published in Ophthalmology.
“Although there have been some studies reporting national or regional [Acanthamoeba keratitis (AK)] incidence rates, a comprehensive assessment of the incidence of this condition is lacking,” Francesco Aiello, MD, PhD, FEBO, FEBOS-CR, a lecturer in the department of experimental medicine’s ophthalmology unit at Tor Vergata University of Rome, and colleagues wrote.
To bridge this gap and aid in prevention and management strategies, the researchers performed a meta-analysis and systematic review to better understand the magnitude and distribution of AK.
The researchers searched PubMed, Scopus and other databases for relevant literature, identifying 105 studies from 28 countries published between 1987 and 2022.
The study’s endpoints included the annualized center incidence (ACI) of AK, defined as the number of AK-affected eyes per health care center per year; meta-analytical ratios of AK eyes both to nonviral microbial keratitis (MK) eyes and to the overall population; and the actual and projected estimates of the number of AK eyes in 2023, 2053 and 2073.
The analysis included 91,951 eyes, 5,660 of which were affected by AK and 86,291 by nonviral MK.
According to results, the median ACI was 1.9. Although Europe had the highest ACI, at 2.75, and South America had the lowest, at 0.8, the researchers reported no significant difference overall in ACI among continents.
Additionally, the ratio of AK eyes relative to the overall number of MK eyes was 1.52%, again with no difference by continent.
The researchers also found that the ratio of AK eyes in relation to the entire population was 0.0002%), which equated to 2.34 eyes per 1 million people.
In addition, they projected a 18.5% increase by 2053, equating to 15,355 AK eyes, and a 25.5% increase by 2073, equating to 16,253 AK eyes, compared with the 2023 baseline of 12,953 AK eyes.
Limitations of heterogeneity of results, publication bias and the limited representation of countries and primary care centers meant each endpoint carried low to very low evidence certainty, Aiello and colleagues wrote.
“Future large-scale, well-designed epidemiological studies are needed to monitor the global trend of AK and further investigate the factors contributing to its incidence,” they added.
Perspective
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AK is a rare but serious disease, as illustrated in this systematic review and meta-analysis, which reported an incidence of approximately 1.9 new cases of AK per center per year. Its consequences are devastating, and it is often very challenging to diagnose and treat.
Diagnosis of AK is typically based on a combination of patient history, clinical examination, culture or corneal biopsy, along with imaging techniques such as confocal microscopy. These modalities can identify Acanthamoeba or differentiate it from other causes of corneal ulcers, such as bacterial or viral infections. The best outcomes are achieved with early diagnosis, but this is challenging due to the rarity of the disease and relatively subtle clinical findings, which can lead to delays of weeks or even months in identifying it.
AK can infect otherwise healthy individuals, most commonly affecting those who wear contact lenses. Most often it is caused by improper use of contact lenses, particularly when contact lenses come into contact with contaminated water sources such as tap water, hot tubs, ponds or homemade solutions. Contact lenses can cause microtrauma to the cornea, which creates an entry point for Acanthamoeba.
Treatment is challenging because the parasite exists in two forms: an active trophozoite and a dormant cystic form. The cystic form is particularly difficult to eradicate, as it is resistant to most therapies. Initial therapy usually involves a prolonged course of antiseptic medications such as chlorhexidine and propamidine, lasting 6 months or more. In many cases, a corneal transplant is necessary to remove the infected tissue and improve visual outcomes.
Despite its relative rarity, it is crucial to consider AK in the differential diagnosis for patients with corneal pathology, especially if they have not responded to standard treatments for more common conditions like bacterial or viral keratitis.
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