zoonoses and communicable diseases common to ... - PAHO/WHO

FOOD POISONING CAUSED BY VIBRIO PARAHAEMOLYTICUS 139Occurrence in Man: Food poisoning caused by this agent occurs sporadically orin outbreaks. Much of the knowledge about this disease is due to researchers inJapan, where the disease was first described in 1953. Subsequent studies showedthat during the summer months, 50% to 70% of food poisoning cases and outbreakswere caused by V. parahaemolyticus (Snydman and Gorbach, 1991).It is difficult to estimate the number of sporadic cases that occur. Many of thosewho fall ill do not see a doctor, and if they do, diagnosis is limited to a clinical examinationwithout laboratory confirmation. Outbreaks can affect few or many people.During an outbreak that occurred in 1978, two-thirds of the 1,700 people whoattended a dinner in Port Allen, Louisiana (USA) fell ill. The source of the outbreakwas probably undercooked shrimp (CDC, 1978). The attack rate of people exposedduring outbreaks in the US varied from 24% to 86% and the number of thoseaffected ranged from 6 to 600. In the four years between 1983 and 1986, there wasan outbreak that affected two people (Snydman and Gorbach, 1991).Another outbreak that affected several hundred people occurred in the Bahamasin 1991. At the most critical point in the outbreak, 348 cases were treated in a hospitalon the island. The outbreak was attributed to a gastropod (Strombus gigas),commonly called “conch,” that the population usually eats raw or partially cooked.Kanagawa-positive V. parahaemolyticus was isolated from 5 of 14 patients’ stoolsamples; two positive cultures were also isolated from eight conch samples.Although the number of cultures was limited, it is thought that V. parahaemolyticuswas the causative agent of the diarrheal disease, which during the entire course ofthe outbreak affected more than 800 people, most of them adults.In British Columbia (Canada), V. parahaemolyticus cultures were isolated from13 patients as well as from 221 environmental samples; 23% and 1.4%, respectively,were Kanagawa positive. The cases of infection contracted locally were urease positiveand Kanagawa negative; the patients who were infected during a trip abroadwere urease negative and Kanagawa positive. Eight percent of the environmentalsamples were also urease positive and Kanagawa negative. These results suggestthat the hemolysin identified by the Kanagawa test is not the only hemolysininvolved in the pathogenesis of the infection (Kelly and Stroh, 1989. Also see thesection on etiology).In Recife, in northeastern Brazil, in 8 (38%) of 21 fecal samples from adultpatients with gastroenteritis, cultures were also isolated that were urease positiveand Kanagawa negative (Magalhães et al., 1991b). Also in Recife, V. parahaemolyticuswas isolated from 14 (1.3%) of 1,100 diarrheal fecal samples. If onlyadult samples are taken into account, the isolation rate would be 7.1%. It was alsopossible to show that the cultures belonged to seven different K antigen serovars(Magalhães et al., 1991a).Occurrence in Animals: V. parahaemolyticus is frequently isolated from fish,mollusks, and crustaceans in coastal waters, throughout the year in tropical climatesand during the summer months in cold or temperate climates.The Disease in Man: The incubation period is from 12 to 24 hours, but may varyfrom 6 to more than 90 hours. The most prominent symptom is watery diarrhea,which becomes bloody in some cases, as has been seen in Bangladesh, the US, andIndia. The other common symptoms are abdominal pains, nausea, vomiting, cephalalgia,and sometimes fever and chills (Twedt, 1989).