As San Diego’s hepatitis A outbreak has continued to grow, so has a fascination about the identity and importance of “patient zero,” the first person believed to be infected in a surge of illness that has now killed 19 people.

At first unwilling to say much about this mysterious person, San Diego County health officials disclosed twice during public meetings in late September that the apparent first patient — what epidemiologists often call an outbreak’s “index case” — was a homeless man who tested positive for hepatitis infection in East County.

Dr. Eric McDonald, chief of the county’s Epidemiology and Immunization Services Branch, reiterated in an email this week that this man was treated in a La Mesa hospital and “when interviewed said that the exposure period was mainly in El Cajon.”

Further details on exactly where in El Cajon, and where else patient zero might have lived, have not been forthcoming and a lack of genetic analysis due to his unknown whereabouts have made absolute confirmation of his first-patient status impossible.

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