Epidemic keratoconjunctivitis is an infection of the eye caused by adenoviruses. The name of the condition stems from the fact that it frequently causes outbreaks, due to its ability to spread from person to person. Redness of the eye, as well as photophobia, blurred vision, ocular discharge, and in some cases, constitutional symptoms such as fever and lymphadenopathy, are described as main complaints. A detailed clinical and microbiological workup is necessary in order to make the diagnosis.
Epidemic keratoconjunctivitis (EK), defined as a highly contagious infection of the eye surface (the conjunctiva and associated tissues), is caused by double-stranded DNA adenoviruses [1] [2]. More than 50 adenoviruses have been described in the literature, but serotypes 8, 19, and 37 are established as main pathogens of EK [2] [3] [4]. Because of their resistance to the majority of disinfectants and heat tolerance (they are able to survive at room temperature), adenoviruses are potent causes of epidemic infections and outbreaks, one of them being epidemic keratoconjunctivitis [3]. Humans are the only known reservoir of adenoviruses, and person-to-person transmission is achieved through direct or close contact with individuals (mainly tear fluids) who are actively shedding the virus when exhibiting signs and symptoms, while some studies have established that individuals remain infectious even a few weeks after resolution of symptoms [1] [2] [3]. After an incubation period that lasts for about 2-12 days, the clinical presentation is distinguished by a severe inflammatory process that leads to redness of the eye accompanied by irritation, excessive tearing and discharge that causes blurred vision, as well as photophobia and a sensation of foreign body presence [2] [3] [5] [6]. EK initially affects only one eye, but it may spread to the other eye as well, although with a much milder presentation [2]. In some patients, generalized symptoms in the form of fever, headaches, proximal lymphadenopathy appear (preauricular lymph nodes are most often involved), but the prognosis is generally self-limiting [2] [3] [5]. EK is predominantly reported in crowded areas (eg. schools, health-care institutions, but also pools due to poorly chlorinated water that contains adenovirus particles) and has no seasonal predilection [2] [6].
The differential diagnosis of eye redness and conjunctivitis is quite broad, but despite the fact that adenoviruses are one of the most important causes of this clinical entity, a thorough clinical investigation is recommended in order to raise suspicion toward an adenovirus infection [5]. Key information may be obtained during history taking when the physician should inquire whether similar symptoms have been reported by other individuals who were in close contact with the patient (eg. classmates, coworkers). Physical examination is an equally important part of the workup, during which eyelid and periorbital edema are observed, in addition to conjunctival hyperemia [2] [3] [5]. A slit-lamp examination performed by a skilled ophthalmologist can further support the diagnosis by detecting conjunctival swelling, hyperemia, and pseudomembrane formation in some cases [2]. When sufficient clinical criteria are obtained, microbiological studies need to be employed. Viral cultures carry a very successful rate of detecting viruses from patient samples, but their rather long turnaround times often requires the use of alternative methods, such as antigen detection through serology and indirect immunofluorescence [5]. But the low specificity and sensitivity of these studies (together with cultures) have placed them in an inferior position compared to newer and faster, but equally sensitive and specific methods [2]. Polymerase chain reaction (PCR), a molecular test that can yield conclusive results within a day, is widely recommended as the main method of diagnosing adenoviruses, although its cost still reduces its overall use in general practice [2] [5] [7] [8].