Management of acute infectious conjunctivitis

ByTerrence P. O'Brien, MD

Whereas the principal causes of acute conjunctivitis are allergic or toxic, a number of microbes can cause acute infectious conjunctivitis as well. These microbes include multiple bacteria as well as viral sources such as adenovirus and herpes simplex virus. This article discusses methods for diagnosing and managing acute infectious conjunctivitis.

Responsible pathogens

A number of different bacterial species can cause conjunctivitis, but four in particular are most often responsible. The four include the gram-positive bacteria Staphylococcus aureus and Streptococcus pneumoniae, and the gram-negative species Neisseria gonorrhoeae and Haemophilus influenzae. The most common of these is S. aureus, which some research has indicated accounts for 33% of cases of bacterial conjunctivitis.

When severe infection is present, it is more likely to be caused by N. gonorrhoeae or H. influenzae; the latter is especially important to consider among pediatric patients.

—Terrence P. O'Brien, MD

Symptoms of acute infectious conjunctivitis include hyperemia of the bulbar and palpebral conjunctiva, irritation, and purulent discharge. Additionally, patients can have mattering of the lids. Severe conjunctivitis has further symptoms including marked lid edema, copious purulent discharge, marked conjunctival hyperemia and signs that are often distinctive of the responsible organism. When severe infection is present, it is more likely to be caused by N. gonorrhoeae or H. influenzae; the latter is especially important to consider among pediatric patients. Among neonates, Streptococcus pyogenes and S. aureus are prime suspects.

Severity determines action

The first step for physicians when it comes to treatment is judging the severity. If the infection is deemed to be nonsevere, it is not generally necessary to obtain a conjunctival culture. It can be treated with a topical antibacterial agent and generally good results are seen with this method. For severe acute infectious conjunctivitis, however, a conjunctival scraping for Gram stain and conjunctival culture should be obtained. Based on the Gram stain and the culture, both topical and systemic antibacterial therapy may be necessary.

H. influenzae conjunctivitis requires special attention, because it can occur in severe form in children. It is frequently seen in the winter months, and it often is marked by violaceous skin hue. It can also be accompanied by upper respiratory illness with fever, discharge and irritability. These cases should be treated immediately with topical antibiotics and systemic antibiotics, such as cefuroxime and azithromycin.

Which agent?

Because antimicrobial resistance has been spreading rapidly,¹ choosing the ideal agent to fight infection is crucial. Such an agent should offer broad-spectrum coverage, should be bactericidal and biocompatible – meaning non-cytotoxic and immunomodulatory – and should be bioavailable with favorable pharmacodynamics (Table 1).

The range of therapeutic agents that have been used in the past is wide. Bacitracin has been used widely; it has a relatively wide spectrum and rarely produced hypersensitivity. It is available only in ointment form, however, which is not a preferable form of administration. Erythromycin has also been used for conjunctivitis and has a low incidence of local side effects. Substantial resistance to this agent has developed, however, and it also is available only in ointment form.

For gram-negative bacteria, aminoglycosides are effective. There is increasing resistance against this agent as well, and more than 15% of patients can have hypersensitivity reactions. There is also a high incidence of keratopathy and inhibition of wound healing.

Fluoroquinolones and macrolides

Fluoroquinolones have gained in popularity as antibiotic agents in recent years; they fulfill all the requirements mentioned above for an ideal agent, although resistance has been increasing. Thus, the fourth-generation agents such as gatifloxacin and moxifloxacin are generally reserved for more serious infections such as keratitis and endophthalmitis.

Another category of agents, the macrolides, have unique pharmacokinetic properties. Erythromycin was the first in this category, developed in 1954, but newer macrolides such as azithromycin have greater activity against gram-positive, gram-negative, and atypical bacteria.

The vehicle of delivery for azithromycin in its eye drop form is the DuraSite (InSite Vision, Alameda, Calif.) bioadhesive, which contains polycarbophil USP and other electrolytes, allowing for a stable formation. Azithromycin is thus able to stay on the ocular surface and is distributed to the tear film, the lids, the corneal tissues, and the conjunctivae. The apparent ability of this agent to achieve high concentrations would require fewer drops over the course of therapy, which increases compliance. Phase 3 trials have indicated good efficacy and safety when azithromycin is used for acute infectious conjunctivitis.²

Acute infectious conjunctivitis is relatively common, but with proper management it can be treated easily. A thorough knowledge of the pathogens responsible and the agents available to treat them is crucial for all physicians who might see patients with this condition.

—Terrence P. O'Brien, MD

As a family of agents, the macrolides also have significant immunomodulatory effects beyond the direct targeting of bacteria. They reduce gene expression of proinflammatory cytokines and adhesion molecules at the transcriptional level; this leads to an inhibition of cytokine production and eventually results in an anti-inflammatory effect.

Summary

References

Mah F. New antibiotics for bacterial infections. Ophthalmol Clin North Am. 2003;16:11-27.
Protzko, E, Bowman L, Abelson M, et al. Phase 3 safety comparisons for 1.0% azithromycin in polymeric mucoadhesive eye drops versus 0.3% tobramycin eye drops for bacterial conjunctivitis. Invest Ophthalmol Vis Sci. 2007;48:3425-3429.