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

234 BACTERIOSEShuman strains. Epidemiological investigation shows that most salmonellosis outbreakscaused by S. typhimurium were caused by a lysotype/biotype that remainedstable throughout the course of the epidemic (Barker et al., 1980). Plasmid profilesand patterns of antibiotic resistance are also useful as epidemic markers.Except for serotypes S. typhi and S. paratyphi A, and S. paratyphi C, which arestrictly human and whose only reservoir is man, all serotypes can be consideredzoonotic or potentially zoonotic.Salmonellae have several virulence factors that contribute to causing diarrhea,bacteremia, and septicemia. These factors include the lipopolysaccharide of theouter wall, pili, flagella, cytotoxin, and enterotoxin (Murray, 1986).Geographic Distribution: Worldwide. S. enteritidis is the most prevalentspecies, followed by S. typhimurium. Changes in the relative frequency of serotypescan be observed over short periods of time, sometimes within one or two years.Only a limited number of serotypes is isolated from man or animals in a singleregion or country. The predominance of one or another can vary over time. Someserotypes, such as S. enteritidis and S. typhimurium, are found worldwide; in contrast,S. weltevreden seems to be confined to Asia.Occurrence in Man: It is very common. Salmonellosis occurs both in sporadiccases and outbreaks affecting a family or several hundreds or thousands of people ina population. The true incidence is difficult to evaluate, since many countries do nothave an epidemiological surveillance system in place, and even where a system doesexist, mild and sporadic cases are not usually reported. In countries with a reportingsystem, the number of outbreaks has increased considerably in recent years; thisincrease is in part real and in part due to better reporting.In 1980, Salmonella was isolated from slightly more than 30,000 people in the US(CDC, 1982). In 1986, 42,028 cases were isolated (Hargrett-Bean et al., 1988). Inthe US and many other countries, the prevalent serotype was S. typhimurium. From1976 to 1993, the rate of isolation of S. enteritidis increased (21% of all isolates) andovertook S. typhimurium as the most common serotype. During the period1985–1991, 375 outbreaks caused by S. enteritidis were reported, with 12,784 cases,1,508 hospitalized cases, and 49 deaths. Most of the cases were sporadic or smallfamily outbreaks, and many of them were from the same phage type, indicating thepossibility of a single source of infection (CDC, 1992a).During a conference held in 1990 that was attended by 1,900 people from 30states in the US, at least 23% became ill with gastroenteritis caused by S. enteritidis.The source of infection was a dessert prepared with eggs that were possibly undercooked(CDC, 1990).In 1985, an outbreak occurred in Illinois (USA) that affected 20,000 people andwas caused by pasteurized milk contaminated by S. typhimurium that was multiresistantto antibiotics (ampicillin and tetracycline).Table 3 shows information on some outbreaks in the period 1981–1985 in variouscountries (WHO Expert Committee on Salmonellosis Control, 1988).According to several authors’ estimates, the number of human cases occurringeach year in the US ranges from 740,000 to 5,300,000. In Canada, the data weresimilar (Bryan, 1981). Rates for reported cases are about 10 per 100,000 inhabitantsin Denmark, 44 per 100,000 in Finland, and 43 per 100,000 in Sweden, one-third totwo-thirds of which were probably contracted by international travelers (Silliker,