Conjunctivitis is inflammation of the conjunctiva, the thin membrane that covers the front of the eye. It may be caused by infection, allergy or an external irritant. People with infectious conjunctivitis usually present with symptoms including an irritated red eye with a watery or purulent discharge. Symptoms often appear in one eye at first and then spread to the other eye. Most people with conjunctivitis are first treated by GPs rather than eye care specialists (Azari and Barney 2013). In England, there were 4.5 million GP consultations concerning the eye in 2011–12 (Health & Social Care Information Centre 2012). It has been estimated that infectious conjunctivitis was responsible for 41% of GP consultations about eye problems (Sheldrick et al. 1993).
Viral infection is the most common cause of infectious conjunctivitis, accounting for up to 75% of cases (Jhanji et al. 2015). Viral conjunctivitis is usually caused by adenovirus, which is highly contagious. Although adenoviral conjunctivitis tends to get better spontaneously, meaning that it is self‑limiting, the person is still infectious for up to 14 to 21 days after infection (Kaufman 2011). Transmission of the infection is mostly by hand‑to‑eye contact, ocular secretions, respiratory droplets, and contact with ophthalmic care providers and their instruments (Azar et al. 1996).
Viral and bacterial conjunctivitis are difficult to distinguish based on symptoms alone. But, because most of the infections are self‑limiting, laboratory confirmation is usually kept for recurrent conjunctivitis, and conjunctivitis that has not responded to medication (The College of Optometrists 2014). Laboratory tests include microscopy and either culture or polymerase chain reaction analysis of conjunctival swabs. The rate of clinical accuracy in diagnosing viral conjunctivitis is less than 50% compared with laboratory confirmation, with many cases misdiagnosed as bacterial conjunctivitis (O'Brien et al. 2009). Only 36% of 300 UK‑based GPs who completed a postal questionnaire believed that they could discriminate between viral and bacterial infection, and there was considerable variability in the use of individual signs to make a diagnosis of infectious conjunctivitis. The same survey found that 95% of GPs usually prescribe topical antibiotics (used to treat bacterial conjunctivitis) for infectious conjunctivitis despite 58% stating that they thought at least half of the cases were caused by viruses (Everitt and Little 2002). Social factors, including the need for children to attend day care or school and for parents to go to work, drive people to seek early treatment and contribute to a GP's decision to prescribe antibiotics for children with acute infectious conjunctivitis (Rose et al. 2006). Antibiotics are not needed for most patients, with 65% recovering without any treatment within 2 to 5 days of symptoms appearing (Rose 2007). Actions taken to slow the development and spread of antimicrobial resistance, including reducing inappropriate prescribing, led to a 3.8% fall in the number of prescriptions for antibiotics in primary care in 2013 compared with 2012 (Health & Social Care Information Centre 2013).
A test that could easily and reliably distinguish between bacterial and viral conjunctivitis could contribute to good antibiotic stewardship if it led to fewer antibiotics being prescribed.