Are natural reservoirs important for cholera surveillance? The case of an outbreak in a Brazilian estuary.

UNLABELLED: Paranaguá Bay is one of the largest estuarine systems on the Southern Brazilian coast. The only recorded cholera outbreak in this region since the early 20th century occurred in 1999 and resulted in 467 cases and at least three reported deaths in a population of approx. 150 000 people. This short communication reports historical, unpublished data related to that outbreak. Water, zooplankton and bivalve samples were collected and evaluated using direct fluorescence assay to determine whether Vibrio cholerae serogroups O1 and O139 were present in the estuarine system at that time. Most of the water (83%) and zooplankton samples (75%) were positive for V. cholerae O1, while V. cholerae O139 was not detected. Shellfish (Mytella sp.) were also positive for V. cholerae O1. These results indicate that the estuary, including biological vectors such as copepods and bivalves, comprise an important reservoir of V. cholerae O1 and a probable waterborne pathway for the disease, in addition to contamination with untreated sewage. SIGNIFICANCE AND IMPACT OF THE STUDY: Despite most of the cholera cases that occurred in Brazil during the 7th pandemic were located in the northern areas of the country, a significant outbreak in Paranaguá, an estuary in the south coast, resulted in at least three deaths in 1999. We report here the detection of Vibrio cholerae O1 in water, zooplankton and bivalve samples during the outbreak, using direct fluorescence assay as an alternative method for the traditional plate culture employed at the time by the Brazilian Sanitary Agency. Results demonstrate that aquatic natural reservoirs comprise a potential route of transmission of cholera, in addition to untreated sewage and routine monitoring is recommended.