The change of etiological agents and clinical signs of epidemic viral conjunctivitis over an 18-year period in southern Taiwan

Background Epidemic viral conjunctivitis is a highly contagious eye disease that occurs worldwide and is caused mainly by adenoviruses and enteroviruses. An 18-year analysis of the changes of pathogens and clinical signs in a subtropical and densely populated island presents certain special features. Methods We retrospectively analyzed the clinical information and laboratory records of the conjunctivitis patients with positive conjunctival swabs from 1980 to 1997. Results The positive rate of laboratory diagnosis of epidemic conjunctivitis was 50.0% (1,233/2,467). From 1980 to 1994, the predominant causative agent of adenoviral keratoconjunctivitis was adenovirus type 8 (Ad8), with six genotypes being evolved. Three of the new Ad8 genotypes each caused a new epidemic. After 1995 the predominant adenoviral pathogens shifted to Ad37 and Ad19, and no more Ad8 was isolated. Enterovirus type 70 (EV70) was isolated from four outbreaks of acute hemorrhagic conjunctivitis (AHC) from 1980 to 1984, but rarely in later years. Coxsackievirus A type 24 variant (CA24v), which first appeared in 1985, appeared later as the causes of four major epidemics of AHC from 1985 to 1994. The overall clinical symptoms of viral conjunctivitis were more severe in the 1990s than in the 1980s. Conclusion In southern Taiwan, outbreaks of adenoviral keratoconjunctivitis caused by new genomic variants could be associated with the long-term endemic co-circulation of Ad8, Ad19, and Ad37, while epidemics of CA24v AHC were caused mainly by introduction of new viral strains from neighboring countries. The aggravation of host symptoms in the 1990s needs further investigation and close follow-up.