Abstract: Objective To estimate the number of secondary cases generated by a primary case of acute hemorrhagic conjunctivitis using epidemic curve data and report on the relative frequency of the symptoms presented, the spatial, the age-specific incidence, and the time from onset of symptoms to diagnosis distributions.

Methods: We analyzed 886 cases of acute hemorrhagic conjunctivitis for which clinical symptoms were fully recorded by public health clinics of the Mexican Institute of Public Health (IMSS) in the state of Colima, Mexico during the period of September - November 2003.

Results: We estimate the number of secondary cases generated by a primary infectious case of acute hemorrhagic conjunctivitis (AHC) to be approximately 4. Most of the AHC cases occurred in the coastal region of the state of Colima, Mexico (93.6%). The most common reported symptom was excessive tearing of the eye or epiphora (92.9%) followed by conjunctival hyperemia (65.8%), photophobia (54.1%), subconjunctival hemorrhage (48.1%), eye pain (47.5%), and palpebral chemosis (36.4%). Less common symptoms were conjunctival edema (24.2%), blurry vision (10.4%) and fever (9.0%). ). The maximum likelihood estimates of the mean and variance for the time of onset to diagnosis were 1.7 days (95% CI 1.59-1.82) and 2.9 days, respectively.

Conclusion: Our estimate of the basic reproductive number (estimated to be approximately 4 secondary cases per primary infectious case) highlights the power of AHC to spread. Therefore, its control should be taken seriously as AHC outbreaks can have important economic consequences. Since there is no specific treatment for AHC, rapid control of AHC relies on contact tracing followed by education of symptomatic infectious individuals.