To treat conjunctivitis, understand how it is spread

July 2005

How is conjunctivitis transmitted? In some cases it is quite obvious. When a baby with gingivostomatitis comes in with a red eye, or a baby develops a purulent conjunctivitis a few days postpartum, these clearly are from direct introduction of the organism into the eye. When a child comes in with acute otitis media (AOM) or pharyngitis, we recognize a common organism causes both but how did they get from the middle ear or the pharynx respectively to the eye? We recognize the frequent concurrence of otitis and conjunctivitis. However, so often the identical species of bacterium causes one or the other or simply resides in the upper respiratory tract causing neither. These may seem trivial questions but to control the spread of conjunctivitis, we must understand how it spreads.

It is generally accepted that conjunctivitis is a very contagious condition. I asked a good friend of mine who had spent many years in the school system how often she had observed classroom epidemics. She responded that they do not occur because the children are excluded as soon as they are found to be affected. This might be somewhat effective in the case of adenovirus conjunctivitis, which usually is accompanied by pharyngitis. How it might impact bacterial conjunctivitis is problematic. Yet do not try to argue with a school nurse about exclusion of children with conjunctivitis or when they can be considered noncontagious and return to school. Most species of the bacteria that cause conjunctivitis can be found in the respiratory secretions of almost all children, sick or well. However, there have been reports in the literature of a strain that was capable of causing wider-spread conjunctivitis.

Lessons learned

During the past few years, we have had reports of outbreaks of conjunctivitis among college students, recruits and elementary school pupils (MMWR. 2003;52[4]:64-66). These outbreaks were so unusual that they were reported in the medical literature. My educator friend was correct: classroom spread is unusual. What made these outbreaks special is that they were caused by pneumococci that produced similar patterns on pulse gel electrophoresis, one that in addition was unencapsulated. What did we learn about how conjunctivitis is spread? As one might have guessed, close contact increased likelihood of spread. Attack rates were higher in classmates and somewhat lower in staff and household contacts. There was relatively little spread to the rest of the community.

What appears to be common to all of these outbreaks was the uncertain effect of measures designed to limit spread.

“The effectiveness of prevention measures for interrupting the transmission of conjunctivitis is not known,” researchers noted. Teachers reported that encouraging increased hand washing was disruptive. Children were excluded an average of two days but admittedly the effectiveness of this measure was difficult to assess. Although antimicrobial eye drops are commonly prescribed, their effect on decreasing spread is unknown. The Red Book states that children can be sent back to school after therapy is initiated. It does not state whether the recommended therapy should be the over-the-counter medication that retails at $5 a pop or some of the newer ones that retail at $100.

There is evidence that bacterial sterilization of the conjunctivae is achieved more rapidly with antibiotic drops than with placebo. How this translates into communicability is unclear. Antibiotics also hasten the resolution of symptoms but some asymptomatic eyes still harbored organisms and others that were still inflamed were sterile (J Pediatr. 1984;104:623).

Thus the decision as to when children should be allowed to return to school is still moot. If one adds up the number of days of parental loss of wages due to the exclusion policy, it would probably be a considerable sum. Certainly children should not be made to attend school if they are too uncomfortable to do so, but keeping them out when the chances of spreading even a highly epidemic strain is less than one in three should make us stop and think.