Vibrio parahaemolyticus O3:K6 Epidemic Diarrhea, Chile, 2005

To the Editor: Outbreaks of diarrhea and gastroenteritis caused by Vibrio parahaemolyticus have been recently reported in many countries and regions where this pathogen was previously unknown (1,2). In mid-January 2005 (Figure), the number of cases of acute diarrhea produced by V. parahaemolyticus dramatically increased in Puerto Montt (41°41′S), a major city in Region X of Chile. The epidemic subsequently peaked in February and then declined with isolated cases in March and April. A total of 3,725 cases of acute diarrhea were detected during the summer months of January–April, 2005 throughout Region X (39°15′S–44°4′S). This epidemic rapidly spread to other urban areas in Region X and to the rest of Chile because Region X is the source of ≈75% of the seafood consumed in Chile. By the end of March 2005, the total number of cases in Chile was 10,783, making this the largest documented occurrence of V. parahaemolyticus diarrhea in the world. Analysis of a questionnaire prepared by the health authority of Region X and completed by 341 patients during January 2005 indicated that all patients had clinical signs compatible with acute diarrhea caused by V. parahaemolyticus (3,4). Stool samples of 60 patients with acute diarrhea were analyzed by standard procedures (5,6). Serotyping confirmed that all V. parahaemolyticus isolates were O3:K6 (5,6), did not produce urease, and showed the Kanagawa phenomenon (virulence-associated hemolysis) (5–8). PCR analysis indicated that the genome of these isolates contained tdh, tlh, and toxRS/new open reading frame 8 DNA sequences and lacked trh sequences (1,8), which are consistent with molecular characteristics of the pandemic clone O3:K6 (1,5–8). Pulsed-field gel electrophore-sis confirmed that V. parahaemolyti-cus strains isolated from patients throughout the epidemic corresponded to pandemic clone O3:K6, as did the strains isolated in Chile from 2 smaller outbreaks in 1998 and 2004 (1,8). Strains of this clone also constituted the only pathogenic strain of V. parahaemolyticus detected in mussels and the only pathogenic strain that has persisted in shellfish throughout this period (1,8). The most common vectors in this outbreak were clams and mussels, not oysters, which reflect the pattern of consumption of shellfish in Chile during the summer (1,8,9). This epidemic in 2005 points to the potential of V. parahaemolyticus O3:K6 to affect many susceptible persons if preventive measures are not taken and enforced quickly (6–9). Temperature and salinity have been reported as factors that influence concentrations of V. parahaemolyticus in the oceans (2,5,7,8). During …