Physicians Guide To RPS Adeno Detector™
Why is it important to differentiate viral from bacterial conjunctivitis?
Contributed by Robert Sambursky
Adenovirus represents the most common form of a red eye worldwide and most frequently presents to the primary care physician. Viral conjunctivitis represents between 15-70% of all causes of infectious conjunctivitis and adenovirus represents close to 90% of these viral cases. However, it is often not easily differentiated from bacterial conjunctivitis. Although viral cell culture is the gold standard, it is rarely performed since it can take days to weeks to obtain a result.
Even though both viral and bacterial conjunctivitis are self-limiting, they have different degrees of contagiousness and associated complication rates. Adenoviral conjunctivitis is extremely contagious. It tends to be associated with urban environments, crowding, daycare, camps, swimming pools, and the military. Adenovirus can be cultured from inanimate surfaces for up to 49 days. Unlike bacterial conjunctivitis that becomes relatively noncontagious after 48 hours of appropriate antibiotic therapy, adenoviral conjunctivitis does not improve with topical antibiotics and continues to shed a significant virus load until the eye is no longer red and tearing. Patients with known adenovirus should be out of school, work, or daycare longer than bacterial disease. This can limit the overall spread of disease.
Bacterial conjunctivitis is rarely associated with complications. Patients that are immunocompromised require more aggressive treatment because bacterial conjunctivitis in this population can rarely generalize into a more systemic condition. Adenovirus has 51 serotypes and serotypes 8, 19, 37 in particular are associated with a more aggressive form of adenoviral conjunctivitis called epidemic keratoconjunctivitis (EKC). Approximately 30-50% of EKC can lead to significant long term morbidity including decreased visual acuity and photophobia from persistent subepithelial corneal infiltrates (superficial corneal opacities), chronic epiphora (tearing) from lacrimal drainage problems, or severe visual loss and pain from a cicatricial entropion associated with symblepharon (shortening and scarring of the conjunctiva) formation. Preventing the transmission of viral disease can limit these complications.
Many patients expect or pressure their physicians to prescribe antibiotics. In some regions, as many as 50% of patients presenting to a primary care provider or emergency room physician may receive unnecessary antibiotic treatment. Antibiotic resistance is also a problem in the eye. Many studies have elicited high rates of antibiotic resistance for Staphylococcal and Streptococcal species with commonly prescribed topical antibiotics including rates respectively approaching 30-40% for erythromycin; 20% of aminoglycosides, and a five-year review study reported that S. aureus resistance to both ciprofloxacin and ofloxacin dramatically increased from 5 percent in 1993 to 35 percent in 1997. In 2000, a study of resistance to Haemophilus influenzae and Streptococcus pneumoniae that caused bacterial conjunctivitis, older medications, such as gentamicin, polymyxin B, neomycin and sulfamethoxazole, were found to be either intermediately or not at all active against these pathogens. Furthermore, antibiotics such as aminoglycosides are toxic to the epithelia and tend to retard healing. For some topical antibiotics, adverse external ocular effects were estimated to be as high as 16%. Up to 8-20% of eyes treated with aminoglycosides will develop a hypersensitivity reaction and become red regardless of the type of infection. A recent 2005 study out of UCSF suggests that topical antibiotics may also contribute to nasopharyngeal antibiotic resistance.
How viral conjunctivitis is best differentiated from bacterial conjunctivitis?
As mentioned earlier, the clinical diagnosis is not often reliable at distinguishing viral from bacterial conjunctivitis. Diagnostic tests available to support a diagnosis fall into two primary categories: traditional tests such as viral isolation or the polymerase chain reaction (PCR) or newer point-of-care diagnostic tests such as the RPS Adeno Detector TM .
Cell culture with viral isolation remains the gold standard. However, cultures of the conjunctiva are rarely performed because of the considerable time delay for viral and/or bacterial isolation results, expense of performing the tests, and the self limited nature of typical conjunctivitis. It does not provide point of care information. However, cultures are the standard procedure in all newborns, neonates, persons who are immunosuppressed, or when Neisseria gonorrhoeae is under consideration as the etiology .
PCR is an excellent means of establishing a reliable diagnosis of acute infectious conjunctivitis. The technique has been shown to be more sensitive, accurate, and rapid than culture for detecting many causes of conjunctivitis. However, PCR is not routinely performed because it is not FDA approved and still requires sending out a sample that may take 1-2 days to process, technical equipment and expertise in running and interpreting samples, and costs much more than viral culture.
The FDA cleared and CLIA waived RPS Adeno Detector TM is the first true point of care test available for conjunctivitis. It can provide a definitive result in 10 minutes and makes a laboratory confirmation of adenoviral conjunctivitis readily available at the time of the patient exam. It works similarly to a pregnancy test or a rapid Strep test for diagnosing Strep throat in children with a sore throat. The RPS Adeno Detector TM can aid health care providers to make an accurate diagnosis, foster patient acceptance of more supportive therapies, identify contagious viral conjunctivitis, and limit spread of disease while simultaneously reducing ocular antibiotic resistance. The management style utilizing empiric antibiotic treatment may not only increase the risk of antibiotic resistance, side effects, allergies, and corneal toxicity, but also may lead to increased cost to the individual and society as a whole.
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[Page updated 1/2011]
