Infectious Diseases


OVERVIEW: What every practitioner needs to know

Are you sure your patient has conjunctivitis?

The typical patient presents with:

  1. Red (or pink) eye - Dilatation of the vessels within the conjunctiva, the normally transparent outer lining of the eye, causes the sclera to appear red.

  2. Exudate - A purulent discharge is very common; it is often associated with swelling of the eyelids, pain and itching. In the morning, the patient may find that that dried exudate has glued the eyelid shut.

  3. Foreign body sensation in the eye - When present, this is usually not as prominent as in keratitis, which poses a greater threat to vision

  4. Photophobia

  5. The cornea and pupil appear normal.

  6. Vision is not impaired.

How did the patient develop conjunctivitis? What was the primary cause of the infection, and how can I distinguish different types clinically?

Conjunctivitis is one of the most common reasons seek help from their primary care health provider. For patients with viral conjunctivitis, there is usually an antecedent upper respiratory infection. Conjunctivitis is extremely contagious, and is easily spread from person to person by touch. See Table I for a complete list of pathogens. The leading causes are:

Table I.

Infectious Causes of Conjunctivitis.
Type of Infection General Symptoms Infecting Agent Comments
Bacterial Thick purulent exudate Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, Neisseria meningitidis, Serratia marcescens, Pseudomonas aeruginosa Petechial hemorrhages may accompany Haemophilus and Streptococcus infections; Gonococcal infections can be severe and progress rapidly, often involving the cornea; Neisseria conjunctivitis can also be severe; the gram negative infections are most common in chronic care facilities.
Viral Serous exudate Adenoviruses, Enteroviruses, Herpes simplex, Varicella, Measles Adenoviruses and enteroviruses are the most common; Herpes may be accompanied by typical herpetic blisters on the eyelid; both Varicella and measles only rarely cause conjunctivitis, and are almost always accompanied by the typical skin lesions
Chlamydial Mucopurulent exudate Chlamydia trachomatis May also have corneal involvement (keratitis)
Fungal Rare, granulomatous Candida, Blastomyces dermatitidis, Sporothrix schenckii Candida is usually seen after use of steroid drops
Parasitic Rare in developed countries Trichinella spiralis, Taenia solium, Schistosoma haematobium, Onchocerca volvulus, Loa loa filariasis Seen in developing countries
  1. Viral infection - The most common cause. The exudate tends not to be highly purulent and more typically is primarily clear and serous. The local lymphatic tissue in the conjunctiva can hypertrophy, forming small smooth bumps called follicles. The disease spreads easily, and the second eye almost always becomes involved within 24-48 hours although unilateral disease does not preclude the diagnosis.

  2. Bacterial infection - Copious quantities of pus usually exude from the eye. The discharge is usually thick and globular.

  3. Chlamydial infection- Conjunctivitis caused by C. trachomatis is one of the leading causes of blindness worldwide. It is rare in the United States, most often occurring in Native Americans. Another form of infection, inclusion conjunctivitis, is transmitted by genital secretions from an infected sexual partner. Inclusion conjunctivitis can also occur in neonates who pass through an infected birth canal. Eyelids and conjunctivae both appear swollen, and there is often exudate. Diagnosis is often made only after time and topical antibiotics have failed to clear the infection.

  4. Fungal infection - Rare. Candidal conjunctivitis occurs most often when the patient has been using corticosteroid eye drops.

  5. Parasitic infection - Rare.

  6. Allergic and toxic causes - Allergic conjunctivitis is very common, usually bilateral, and very itchy. Common toxic causes include almost any topical solution applied to the eyes. Hard and soft contact lenses and cosmetics are also frequent offenders.

  7. Miscellaneous causes - Conjunctivitis can accompany Reiter's syndrome, keratoconjunctivitis sicca, graft-versus-host disease, and pemphigoid.

Which individuals are of greater risk of developing conjunctivitis?

Individuals at particular risk of recurrent conjunctivitis include those with diminished tear production (dry eyes), such as those with scleroderma or Sjogren's syndrome.

Beware: there are other diseases that can mimic conjunctivitis.

Conjunctivitis must be differentiated from other, often more serious, causes of red eye. The most important confounder is keratitis that can lead to endophthalmitis, inflammation of the inner structures of the eye, which can lead to impaired vision and even blindness. In the latter, eye pain - often described as the feeling of a foreign body in the eye - is the most prominent symptom. Conjunctivitis, however, also can be associated with a foreign body sensation.

Other causes of red eye that must be considered include episcleritis, uveitis , blepharitis and subconjunctival hematoma. Acute angle closure glaucoma is a medical emergency that presents with red eye, severe eye pain, headache and often systemic symptoms, such as nausea and vomiting. A crusting exudate does not accompany this disease.


The patient who presents with typical viral or bacterial conjunctivitis does not require any lab tests.

In severe cases, or when the diagnosis is in doubt, conjunctival scrapings can be obtained for Gram stain and culture. Cultures are also recommended for immunosuppressed patients and anyone who has not responded to therapy within about 7 days.

Gram stain will reveal a mononuclear cell exudate in viral conjunctivitis, whereas an abundance of polymorphonuclear leukocytes (PMNs) will be seen in bacterial and chlamydial disease. Follicular inflammation combined with an exudate containing PMNs strongly suggests chlamydial infection. The exudate of allergic conjunctivitis may show an abundance of eosinophils.

What imaging studies will be helpful in making or excluding the diagnosis of conjunctivitis?

No imaging studies are required in the evaluation of conjunctivitis. Rarely, a CT of the sinuses may be helpful if you suspect extension of bacterial infection from the sinuses.


Routine conjunctivitis can be easily managed by primary health care providers. However, if the diagnosis is in doubt, and particularly if there are any features suggestive of a more serious condition (e.g. keratitis or acute angle closure glaucoma), urgent referral to an ophthalmologist is necessary.

What treatments are recommended for conjunctivitis?

1. Anti-infective agents:

  1. Viral and allergic conjunctivitis - Antibiotic drops play no role here. Topical agents such as antihistamine and decongestant eye drops as well as simple artificial tears and cool, moist compresses may provide significant relief. Oral antihistamines can also be helpful.

  2. Bacterial conjunctivitis - Although bacterial conjunctivitis is usually self-limiting, most clinicians prefer to treat with topical drops. Systemic antibiotics are only used in extremely severe cases (e.g. in case of severe pain and visual compromise) and those with presumed systemic disease (e.g. gonorrhea). Many ophthalmologists now choose as their first choice a flouroquinolone eye-drop (e.g. moxifloxacin 0.5% TID x 7d), which leads to rapid clinical improvement and treats both gram-positive and gram-negative pathogens. It is a particularly good choice for contact lens wearers. Alternative topical agents include gentamicin and tobramycin for gram-negative infections, polymyxin B- bacitracin, neomycin-polymyxin, polymyxin B-trimethoprim, or erythromycin for gram-positive infections. Many of these alternatives are also far less expensive than the fluoroquinolones.


A simple algorithm can help distinguish those infections that should be treated with empirical topical antibiotics from those that should not. It relies on 3 questions:

  1. Does your eyelid stick closed in the morning (+5 points)?

  2. Does your eye itch (-1)?

  3. Have you had recurrent conjunctivitis (-2)?

A score of 5 increases the probability of bacterial conjunctivitis from 33% to 77%. A score of -3 lowers the probability to 4%.

How long is conjunctivitis contagious, and how can I prevent its spread?

Patients with viral conjunctivitis can be contagious for up to 2 weeks. They should be encouraged to wash their hands frequently, avoid touching their face as much as practical, and should not share personal items, such as towels and eating utensils, with others. Contact lenses worn just prior to and during the infection should be discarded, and further contact lens wearing discouraged until the infection has resolved. Patients who work in the food industry and health care workers should not be allowed to return to work until they no longer have any ocular discharge.

What's the evidence?

Epling, J. "Bacterial conjunctivitis". Clin Evid (Online). 2012.

Everitt, HA, Little, PS, Smith, PW. "A randomised controlled trial of management strategies for acute infective conjunctivitis in general practice". Bmj. vol. 333. 2006. pp. 321.

Leibowitz, HM. "The red eye". The New England journal of medicine.. vol. 343. 2000. pp. 345-351.

Rietveld, RP, ter Riet, G, Bindels, PJ, Schellevis, FG, van Weert, HC. "Do general practitioners adhere to the guideline on infectious conjunctivitis? Results of the Second Dutch National Survey of General Practice". BMC Fam Pract. vol. 8. 2007. pp. 54.


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