Epidemic kerato-conjunctivitis--do outbreaks have to be epidemic?

To study: the epidemiology of an outbreak of adenoviral keratoconjunctivitis in a UK teaching hospital; disease presentation and its effect on clinical diagnostic efficiency; patterns of viral transmission between staff and patients; the effectiveness of infection control procedures in minimising outbreaks.

Prospective/retrospective clinical audit and retrospective audit of virological culture results: all viral culture swabs taken during an outbreak of adenoviral keratoconjunctivitis were analysed. The case records of patients whose viral swabs were positive for adenoviral culture were traced. The time for viral cultures to become positive (culture positive time) was calculated. Analysis of the case notes was performed to elucidate (1) the source of infection and (2) the risk factors for acquisition of the infection. Retrospective clinical audit was performed to evaluate the effectiveness of infection control procedures. Adenovirus isolates underwent serotyping.

During the 3-month period of study, there were 38 confirmed cases of adenoviral keratoconjunctivitis. This represented a 217% increase in the number of new cases per 3-month period. The case notes for five patients were untraceable. Of the remaining 33 patients, 21 (63%) had acquired their infection either directly or indirectly from the eye department and 22 (67%) had presented with unilateral disease. The rate of misdiagnosis was higher (9/22=42%) in patients presenting with unilateral disease than those presenting with bilateral disease (2/11=18%). Intradepartmental acquisition of infection was associated with invasive procedures, for example use of diagnostic/therapeutic contact lenses. Culture positive times ranged from 3 to 29 days. The introduction of infection control procedures was associated with a dramatic decrease in the incidence of departmentally acquired cases with no new cases after 2 weeks. Multiple serotypes of adenovirus were involved.

Outbreaks of adenoviral keratoconjunctivitis are a serious public health issue concerning ophthalmic departments. This audit study illustrates several important points: (1) how hospital-acquired infection can account for a significant proportion of the cases seen, (2) how multiple types of adenovirus can be involved in a single outbreak, (3) that severe unilateral disease is associated with a higher rate of misdiagnosis; and (4) how standard viral culture techniques may not be satisfactory in confirming/disproving infection when the diagnosis is in doubt. The potential benefit of infection control procedures in minimising this outbreak could not be proven within this audit.