Conjunctivitis can result from many causes. These causes include viruses, bacteria, allergens, contact lens use (especially the extended-wear type), chemicals, fungi, and certain diseases.
Infected children should be allowed to remain in school once any indicated therapy is implemented, except when viral or bacterial conjunctivitis is accompanied by systemic signs of illness. However, infected students should refrain from attending school if their behavior is such that close contact with other students cannot be avoided (Red Book).
Viral ConjunctivitisViral conjunctivitis can be caused by the following viruses, with adenoviruses being the most common cause:
Viral conjunctivitis is highly contagious. Most viruses that cause conjunctivitis are spread through direct hand-to-eye contact by hands that are contaminated with the infectious virus. Hands can become contaminated by coming in contact with infectious tears, eye discharge, fecal matter, or respiratory discharges.
- Picornaviruses, such as enterovirus 70 and coxsackievirus A24
- Rubella virus
- Rubeola (measles) virus
- Herpesviruses, including
- Herpes simplex virus
- Varicella-zoster virus, which also causes chickenpox and shingles
- Epstein-Barr virus, which also causes infectious mononucleosis (mono)
- Newcastle disease virus, a virus that infects birds but that can also cause conjunctivitis in humans exposed to infected birds
Bacterial ConjunctivitisThe bacteria that most commonly cause bacterial conjunctivitis in the United States are
- Staphylococcus aureus
- Haemophilus species
- Streptococcus pneumoniae
- Pseudomonas aeruginosa
Globally, the bacterium Chlamydia trachomatis (trachoma) is the leading cause of preventable blindness of infectious origin. Trachoma is a chronic follicular conjunctivitis, which is transmitted from person-to-person, through shared items or by flies. Learn more about trachoma and other hygiene-related diseases.
Topical antimicrobial therapy is indicated for bacterial conjunctivitis, which is usually distinguished by a purulent exudate.
Allergic conjunctivitis is common in people who have other signs of allergic disease, such as hay fever, asthma, and eczema. It is caused by the body’s reaction to certain substances to which it is allergic, such as
- Pollen from trees, plants, grasses, and weeds
- Dust mites
- Animal dander
- Contact lenses and lens solution