Is it possible to detect the presence of adenovirus in conjunctiva before the onset of conjunctivitis?

It is widely accepted that patients with adenoviral conjunctivitis are contagious approximately as long as 14 days after the onset. However, there is controversy about whether patients with adenoviral conjunctivitis are contagious during the incubation period. We investigated the potential of the eye as a source for spreading infection during the incubation period by analysing the presence of adenovirus (Ad) in contralateral eyes before onset in patients with bilateral adenoviral conjunctivitis using the immunochromatography (IC) test and polymerase chain reaction (PCR). Patients with adenoviral conjunctivitis were directed to visit an outpatient clinic at approximately 3-day intervals until onset in the contralateral eye or 2 weeks after onset in the first eye. Conjunctival scrapings obtained from the first infected eye and the contralateral eye before and after onset were tested to detect Ad antigen using the IC test and PCR. Out of the 32 cases, 23 (72%) developed conjunctivitis in the contralateral eye. Among these bilateral cases, 18 (78%) were found positive for Ad by PCR after onset in the contralateral eye. However, no specimen obtained before onset showed a positive result for Ad in both tests. Although there is a possibility that eyes are contagious during the incubation period of adenoviral conjunctivitis in some situations, these results suggest that the possibility of the eye acting as a source for spreading infection during the incubation period is very small.