Thirty-five cases of P. vivax malaria occurred among a group of Camp Fire girls who attended the 1952 summer camp at Lake Vera, Nevada County, California. Nine of the cases experienced primary attacks 10 to 40 days after exposure. Twenty-six exhibited latent periods of 217 to 316 days. The probable source of these infections was traced to a recently returned Korean veteran.
The occurrence of this outbreak demonstrated the vulnerability of this country to the introduction of malaria from abroad when favorable circum-stances exist, and it provided an unusual opportunity to observe the natural history of the P. vivax strain of malaria in a nonimmune population living in a nonendemic area.
The investigation confirmed, extended, and elucidated the knowledge on latency and delayed primary attacks exhibited by certain strains of temperate zone malaria. The documentation of the incubation periods substantiated the observation that many P. vivax infections contracted in autumn may remain clinically latent for eight to nine months.