Conjunctivitis

Make the Diagnosis: Does This Patient With Acute Infectious Conjunctivitis Have a Bacterial Infection?

Prior Probability of Viral vs Bacterial Conjunctivitis

Once infectious conjunctivitis is clinically suspected, the clinician must assess the likelihood of viral vs bacterial conjunctivitis. A key factor is the age of the patient. In studies that included children (mean age, 4.7 years; range, 1 month to 18 years), bacterial conjunctivitis was present in 71% while viral conjunctivitis was present in only 16%; 13% were attributed to other causes that were culture negative, chlamydia, or ultimately judged to be allergic. Among adults (mean age, 25.7 years), the prevalence of viral conjunctivitis was 78% while bacterial conjunctivitis was present in 16%; 6% were attributable to other causes (including herpes simplex and chlamydia).

Population Among Whom Viral or Bacterial Conjunctivitis Should Be Considered

Conjunctivitis is common and patients usually present for care with ocular redness and discharge. Other common causes of red eye that usually can be distinguished clinically from infectious conjunctivitis are allergic conjunctivitis (though most patients do not seek medical care)¹, subconjunctival hemorrhage, and dry eye disease. Serious but less frequent causes of ocular redness include foreign body, corneal abrasion, corneal infection, scleritis, iritis, and glaucoma. For practical purposes, the presence of a red eye with discharge indicates infectious conjunctivitis in the majority of cases, and it requires clinicians to assess the likelihood of a viral vs a bacterial etiology.

Assessing the Likelihood That the Patient Has Bacterial Conjunctivitis

Most studies of conjunctivitis are reports of large case series where only the sensitivity can be determined. Among the most frequently studied findings, the highest sensitivities for viral conjunctivitis were conjunctival follicles (77%; 95% CI, 36%-96%), watery discharge (77%; 95% CI, 33%-96%), eyelid swelling (59%; 95% CI, 19%-90%), bilateral eye symptoms (44%; 95% CI, 33%-56%), and pharyngitis (43%; 95% CI, 28%-59%). Among the most frequently studied findings for bacterial conjunctivitis, the most sensitive findings were the patient reported having their eyelids stuck together on awakening (86%; 95% CI, 67%-95%), mucopurulent ocular discharge (67%; 95% CI, 48%-82%), and bilateral eye symptoms (59%; 95% CI, 44%-72%).

Studies that included patients with either viral or bacterial conjunctivitis can be evaluated to determine which findings distinguished a viral etiology for conjunctivitis from a bacterial etiology. The most useful findings for viral conjunctivitis included the presence of pharyngitis (LR range, 5.4-9.9), preauricular lymphadenopathy (LR range, 2.5-5.6), and contact with another person with red eye (LR, 2.5; 95% CI, 1.6-3.7). For bacterial conjunctivitis, the presence of mucopurulent ocular discharge (LR, 2.1; 95% CI, 1.7-2.6) and otitis media (LR, 2.5; 95% CI, 1.5-4.4) were associated with the presence of bacterial conjunctivitis. The presence of a watery discharge (LR, 0.03; 95% CI, 0.004-0.26) or pharyngitis (LR range, 0.10-0.19) was associated with a lower likelihood of bacterial conjunctivitis. (See Table 111-1.)