The disease has been reported most often in the southwestern areas of the country. Incidence has been estimated as high as one half of the population in endemic areas. Prevalence is not influenced with regard to sex or race, but children aged 10-14 years are at highest risk. The cornea can exhibit superficial epithelial changes. The symptoms are pain and irritation, and the lids and periocular tissues present with marked inflammation.
Some investigators speculate that epidemics can begin when group immunity falls below a safe level.
A study of change of neutralizing antibody with time was described after the 1984 epidemic of AHC in Sapporo, Japan. AHC has been noted throughout the tropical regions of the world without regard to race. It has been the cause of worldwide pandemics. It also has been reported in Pakistan, Thailand, and the Middle East. As noted before, children aged 10-14 years have been found to have the highest rate of positive neutralizing antibodies to CA24 and EV70.