Bacterial Conjunctivitis (Pink Eye)

Updated: Feb 07, 2023
  • Author: Karen K Yeung, OD, FAAO; Chief Editor: Andrew A Dahl, MD, FACS  more...
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Practice Essentials

Conjunctivitis, which is defined as inflammation of the bulbar and/or palpebral conjunctiva (the transparent lubricating mucous membrane that covers both the surface of the eye and lining of the undersurface of the eyelids), has many etiologies, including infection from various bacteria, fungi, and viruses, as well as toxic and allergic insults. [1] Conjunctivitis, which is also known as pink eye, is common; about 1% of all primary care office visits in the United States are related to conjunctivitis, affecting about 6 million people annually. [2, 3]

Only about 30% of primary care patients with infectious conjunctivitis are confirmed to have bacterial conjunctivitis, although 80% are treated with antibiotics. [4] The bacterial etiology often depends on geography and age, but the most common include Staphylococcus, Streptococcus, Corynebacterium, Haemophilus, Pseudomonas, and Moraxella species. [5]

Complications can range from mild corneal irritation to severe visual loss, which develops in cases caused by extremely pathogenic bacteria, such as Chlamydia trachomatis or Neisseria gonorrhoeae. Bacterial conjunctivitis has been estimated to account for between $377 and $875 million annually in healthcare costs in the United States. [6]

Signs and symptoms

Signs and symptoms of bacterial conjunctivitis, beyond injected and edematous (inflamed) conjunctiva, include the following [5] :

  • Follicles are more often a sign of ocular viral infections; may also occur with chronic allergic or hypersensitivity conjunctivitis
  • Papillae on the injected tarsal conjunctiva, also seen in viral conjunctivitis and ocular allergy (see below)
  • Discharge: More purulent than in viral conjunctivitis, with more mattering (generally white, green, or yellow mucous discharge) of the eyelid margins and greater associated difficulty prying the eyelids open following sleep; patients may report waking up with their eyes “glued” shut
  • Enlarged preauricular lymph node: Common in viral conjunctivitis and unusual in bacterial conjunctivitis, although found in severe bacterial conjunctivitis caused by N gonorrhoeae
  • Eyelid edema: Often present in bacterial conjunctivitis, but mild in most cases; severe eyelid edema in the presence of copious purulent discharge raises the suspicion of N gonorrhoeae infection

See Clinical Presentation for more detail.


Routine bacterial culture is indicated for specific cases of clinically suspected bacterial disease. These are best obtained with a commercially available sterile red-top culturette using applicators that contain artificial fiber, rather than cotton-tip applicators, which have bacteriostatic properties. Although most routine cases of bacterial conjunctivitis should not require culture confirmation, certain presentations, such as the following, suggest utility to the astute clinician:

  • Neonatal conjunctivitis
  • Hyperacute conjunctivitis suggestive of N gonorrhoeae
  • Extremely elderly patients
  • Nursing home patients
  • Immunocompromised patients: HIV infection, chemotherapy, immunosuppressive therapy
  • Recurrent or recalcitrant conjunctivitis
  • Corneal allograft recipients
  • Patients who have undergone recent intraocular surgery: pars plana vitrectomy, cataract, glaucoma shunt
  • Patients with a thinning or damaged trabeculectomy filtering bleb
  • Methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant Staphylococcus epidermidis (MRSE) carriers

Conjunctival scrapings are often used in the diagnosis of bacterial conjunctivitis; they can be collected with topical anesthetic and gentle use of a platinum spatula or similar blunt metallic object.

Gram stain is useful for identifying bacterial characteristics, including a rough bacterial titer, a rough estimate of white blood cell (WBC) count, and the presence of chains, clusters, or intracytoplasmic inclusions.

Giemsa stain is helpful in screening for intracellular inclusion bodies of Chlamydia.

Cultures can be completed for chlamydial and other bacterial organisms, as well as for viral agents. Fungal culture would be unusual except in the setting of a corneal ulcer, a vegetative or gardening injury, or in the case of known contamination of a contact lens solution. The cellular response in conjunctivitis differs according to the cause, as follows:

  • Bacterial infections: Neutrophils predominate
  • Viral infections: Lymphocytes predominate
  • Allergic reactions: Eosinophils predominate

See Workup for more detail.


The mainstay of treatment for bacterial conjunctivitis is topical (administered as eye drops or ointment) antibiotic therapy. Systemic antibiotics are indicated for gonorrhea and chlamydial infections. Under certain circumstances, topical antibiotics may be considered of limited benefit and, considering the risks of widespread antibiotic resistance, should be withheld while the disease course resolves without treatment. [7, 8, 9]

Steroid use is controversial (see Treatment for more details).

Povidone-iodine 1.25% ophthalmic solution may be a safe and viable alternative to topical antibiotics for treating bacterial conjunctivitis, [10] especially in resource-poor countries, where antibiotics may be scarce and/or expensive. A product that contains both povidone iodine 1% and dexamethasone 0.1% is in phase III clinical trials for the treatment of viral and bacterial conjunctivitis (Shire, Dublin, Ireland).



Conjunctivitis of the bulbar and/or palpebral conjunctiva can be caused by allergies, toxins, fungi, viruses, or bacteria.

Bacterial conjunctivitis due to gram-positive bacteria such as Staphylococcus aureus or Streptococcus pneumoniae is generally milder than conjunctivitis caused by gram-negative bacteria. Mild conjunctivitis is usually benign and self-limited and can be monitored without treatment or easily treated with antibiotics. Gram-negative conjunctivitis is caused by bacteria such as Pseudomonas, Serratia marcescens, Haemophilus influenzae, Moraxella, C trachomatis, and N gonorrhoeae. Gram-negative causes of conjunctivitis are especially virulent and can lead to severe infections of the cornea and possible ocular perforation within 24-48 hours of infection. Severe conjunctivitis can cause blindness and can signify a severe underlying systemic disease.

The purpose of this article is to (1) help the practitioner recognize the characteristics and significance of bacterial conjunctivitis, (2) avoid pitfalls in diagnosis, and (3) convey appropriate treatment modalities.

Conjunctival scrapings and cultures are commonly used to guide treatment choices and confirm the microbe in severe bacterial conjunctivitis and cases that are resistant to antibiotic treatment (see Workup). The mainstay of treatment of bacterial conjunctivitis is topical antibiotic therapy. Systemic antibiotics are indicated for N gonorrhoeae and chlamydial infections. Surgical intervention is required only if the cornea is involved and results in corneal opacification (see Treatment).

See the following for more information regarding the differential diagnoses of bacterial conjunctivitis:



The surface tissues of the eye and the ocular adnexa are colonized by normal flora such as streptococci, staphylococci, and corynebacteria. Alterations in the host defense, in the bacterial titer, or in the species of bacteria can lead to clinical infection. Alteration in the flora can also result from external contamination (eg, contact lens wear, swimming), the use of topical or systemic antibiotics, or spread from adjacent infectious sites (eg, rubbing of the eyes).

The primary defense against infection is the epithelial layer covering the conjunctiva. Disruption of this barrier can lead to infection. Secondary defenses include hematologic immune mechanisms carried by the conjunctival vasculature, tear film immunoglobulins, and lysozyme and the rinsing action of lacrimation and blinking.



Bacterial conjunctivitis most often occurs in otherwise healthy individuals. Risk factors include exposure to infected individuals, fomite contact (eg, towels, napkins, pillow cases, slit-lamp chin rests and handles), contact lens wear, sinusitis, immunodeficiency states, prior ocular disease, trauma, and exposure to agents of sexually transmitted disease at birth.

Contact lens use is commonplace and thus deserves special consideration. It is known that contact lens wear, especially sleeping while wearing the lenses, is a common risk factor for bacterial corneal infection, especially in developed countries where contact lens use is more prevalent. [11] Risks for bacterial corneal infection in contact lens wearers are also known to increase with improperly maintaining contact lens integrity and contact lens case hygiene, failing to discard the contact lenses in a timely manner, and exposing the contact lenses to water (eg, swimming, showering, tap water). Allergic conjunctivitis in contact lens users is also common, and differentiation is important for appropriate treatment. It is usually prudent to treat suspected bacterial conjunctivitis in contact lens users, including discontinuing use of lenses and prescribing topical antibiotics.



Bacterial conjunctivitis is common worldwide. The estimated incidence of bacterial conjunctivitis in the United States is 135 cases per 10,000 population annually, [6] constituting approximately 1% of all primary care consultations. [12] ​Internationally, isolated epidemics can be devastating in areas affected by blinding infections of newborns, especially in areas heavily affected by C trachomatis, [13] which can cause blindness in up to 8% of the population. [14] Staphylococcal infection was the most common etiology in Paraguay, [15] Pseudomonas in Thailand, [16] and streptococci in India. [17]

Racial and sexual differences in incidence

Bacterial conjunctivitis occurs in persons of all races, although differences in frequencies may be reflected by geographic variations of pathogen prevalence.

Males and females have equal natural resistance to bacterial conjunctivitis. Differences in infection rates may reflect environmental and behavioral patterns, such as the higher rate of contact lens use among women.

Age-related differences in incidence

Age is a relevant factor in the prevalence of bacterial conjunctivitis. In the United States, bacterial conjunctivitis is more prevalent in children than in adults; 23% of cases are reported in children aged 0-2 years, 28% in children aged 3-9 years, and 13% in children aged 10-19 years. Adults account for 36% of cases. [6, 18]  H influenzae is the most common pathogen in children, followed by S pneumoniae, S aureus, and Moraxella catarrhalis. In adults, S aureus, H influenzae, S pneumoniae, and Moraxella species are the most common pathogens; MRSA prevalence has been increasing in nursing homes.

The practitioner must be vigilant in considering sexually transmitted diseases caused by N gonorrhoeae and Chlamydia in sexually active age groups and in newborns who may have been exposed during birth. Tactful and confidential history taking are a necessary skill in order to avoid violating HIPAA regulations. In an ethical or medicolegal situation, obtaining advice from administration and/or colleagues is recommended.



The prognosis for complete recovery without sequelae is excellent in bacterial conjunctivitis, as long as the cornea is not involved. Most benign cases are treated with topical antibiotics or self-resolve. [19] Bacterial conjunctivitis generally resolves within 1-2 weeks without treatment. Complications are expected to develop only in cases caused by extremely pathogenic bacteria, such as C trachomatis or N gonorrhoeae.

Mortality in the setting of bacterial conjunctivitis is related to the failure to recognize and treat the underlying disease. Sepsis and meningitis caused by N gonorrhoeae can be life-threatening. [20] Chlamydial infection in the newborn can lead to pneumonia and/or otitis media. [21]

Signs and symptoms of discomfort, mucopurulent ocular discharge, and conjunctival redness are common in benign cases and often lead to absence from work and school to minimize the risk of infection to others. Morbidity can be associated with misdiagnosis. Since many eye diseases cause the eye to be red, it is beneficial to have a solid clinical approach to differential diagnoses of the red eye, as well as an effective referral paradigm in the primary care setting. Diagnoses often missed by non–eye-care providers (providers other than ophthalmologists and optometrists) include acute glaucoma; iritis; bacterial, fungal, and parasitic keratitis; corneal foreign bodies; conjunctival and tarsal foreign bodies; herpetic dendritic keratitis; scleritis; and subconjunctival hemorrhage, among others.


Patient Education

To prevent bacterial conjunctivitis, patient education should include good hygiene (eg, washing hands with soap and water) and avoidance of touching the eyes, especially after exposure to potentially infectious sources. Proper contact lens care includes avoidance of contact lens wear while sleeping and proper cleaning and discarding of both lenses and contact lens cases.

Patients with bacterial conjunctivitis should be instructed not to touch their eyes and to avoid sharing fomites. They should also be educated regarding their infectious nature to prevent transmission and the importance of finishing their antibiotic regimen. Patients with bacterial conjunctivitis who wear contact lenses should be instructed to discontinue contact lens use and to discard their used contact lenses, open contact lens solutions, used contact lens cases, and used makeup and makeup brushes.