Typhoid Case Study Schenectady

Unformatted text preview: CASE §TUDY~ ANALYSIS OF A FOOD-BORNE EPIQEMIC Typhoid in Schenectady On June 20, 1939, the Health Ofiicer of Schenectady, a city with a population of approximately 90,900, received case reports of 5 cases of typhoid fever in residents of the city. On the same day he had received an inter-state notification of a case of typhoid fever in a resident of another state who had beena resident of his city during . approximately three of the four weeks preceding the onset ofthe illness. Typhoid fever had not occurred in this city during that year prior to the report of these cases. The ' average annual number of cases reported in this city during the preceding five years was two cases per year. ' ' The water supply of the city is a surface supply obtained from a stream draining from a relatively uninhabited section. Approximately eight years prior to the epidemic, a modern rapid sand filtration plant was installed and the supply was chlorinated. The operation of the purification plant under the supervision of a competent sanitary engineer. The health officer received daily reports of bacteriological analyses of water from six points in the distribution system. The city was completely sewered and between 95% - 98% of the houses within the city limits were connected with the city sewer system. By city ordinance, the sale of milk other than pasteurized or certified milk was prohibited. There were two large dairies supplying approximately 75% of the milk in the city; all of this milk was pasteurized. There was one other that distributed approximentaly three hundred quarts of pasteurized milk daily. A small but undetermined amount of unpasteurized milk was purchased in customers’ containers from farmers living just outside the city limits. Two large manufacturers who also supplied several other cities and the surrounding area supplied approximately 95% of the ice cream used in the city. Shellfish dealers were licensed by the City Health Department and were required to keep records of receipt and distribution of all stock handled. Twenty—one chronic typhoid carriers were known to the City Health Department and were under nominal supervision of that department. A survey of the hospitals of the city and a canvass of all physicians revealed a total of thirteen known or suspected cases of typhoid fever (including the case reported from a nearby state). Epidemiologists’ data were collected by means of visits to these patients and to the homes of the patients hospitalized. A spot map of the cases showed no concentration of any areas Table 1 presents a summary of the important information gained from the preliminary investigation of each of the thirteen reported cases. Question #1: What possible important facts tie together these cases? Whichdf these seem most significant? . 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Cemetery in Schenectady, followed by a late afternoon supper which was served to thirty—three of the persons attending the Memorial Day service. The food served at this supper was prepared by a number of those attending and was served as a buffet supper. Each individual attending the supper was interviewed, and as accurate as possible a record of the foods consumed by each was obtained. Previous history of typhoid fever, or suggested symptoms, as well as information concerning the preparation of serving of food was obtained. An attempt was made to obtain fecal specimens from all individuals attending the supper and a series of at least three specimens was obtained from all persons known to have supplied the food for the supper. No histories of clearly significant illness were obtained. Laboratory studies, chiefly positive stool cultures, confirmed the clinical diagnosis of typhoid in all 13 cases. In addition the following laboratory data of interest were obtained for persons who attended the picnic but who remained well: Irene Pickett: Positive stool on 7/4, 7/5, and 7/6; negative stool on 7/23, and 8/2. Margaret Bennett: 11 consecutive positive stool, 7/2 through 10/4. Kenneth Rhinheardt: Positive stool 7/4; three latter stools were negative. Question #5: Consider the status of each of these people. Among them, who was likely to have been infected during this outbreak? Who previously? Question #6: What laboratory test might be done now which were not available' in 1939? How might these help? ' Table 2 represents data on the case status of the 35 individuals attending the supper, the foods that each person ate, and infonnation concerning the source of each food item. voom asp :mme we: mc_>m; umpfimomg n o _ . . woo; ecu :mpmm m=w>mz umwfiuuog u + umuuuop no: u 9 “zones mLOHW mcooh n % $93,: .2: 3 25; 295.3 88 BM. ... 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Question #7 : Use the blank table labeled “Food Specific Attack Rates.” Indicate attack rates for persons eating (and those not eating) each food. Compute risk for each food. Include data from all 35 individuals. Question #8: From the menu, list the foods which you think would be most susceptible to mass contamination (specially thoseproviding a good growth medium, hence of high risk contamination during handling and serving) and those you think would be least susceptible. Question #9: From your completed table of food-specific attack rates, determine the foods most likely to be involved in this outbreak, considering: ' a) a majority of the c'ases should have eaten the food b) the relative risk of infection for those who ate the food; and c) the ease of mass contamination of the food. Question #10: How should you handle the data for persons who cannot recall whether or not they ate a particular food? Question #11: Why are we concerned about attack rates among persons who did not eat particular food? Question #12: To incriminate a particular food, what findings would you expect? Question #13: Taking all the evidence into consideration, what is the most probable explanation for this outbreak? Be specific: what food (or foods) was'involved? Which person was involved? Question #14: Are there important gaps in the evidence? Question #15: What measures would be useful in helping to prevent similar future outbreaks? Table'#3 ' r _ Food-Specific Attack Rates Persons Without Disease " Persons with Disease Potato Eating Salad Not Eating Unknown Eating Not Eating Unknown Cabbage Eating Salad Not Eating Unknown Spiced Eating Ham Not Eating Unknown Baked Eating Beans Not Eating Unknowu Rolls Eating Not Eating Unknown Cakes Eating Not Eating Unknown Coffee Eating Not Eating Unknown Eating Not Eating Unknown Eating Not Eating Unknown Macaroni Salad Summer Sausage ...
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Case Study – Analysis of Food Borne Illness Lab 5 Miranda Fraraccio Erin Ross ChrisTna ±onucci Jennifer Smith Q#1 what possible important facts Te together these cases? Which of these seem most important? Some important facts that Te the cases of typhoid fever together were that nine out of the thirteen cases were on city water nad sewer, ten out of the thirteen were female, and eleven out of the thirteen were at the Memorial Day picnic. ±he fact that eleven out of the thirteen cases went to the Memorial Day picnic seems to be the most important. Q#2 prepare a chart showing the chronology of the outbreak by date of onset of each case. What kind of curve does this represent? From this chart can you esTmate a possible date of common exposure? Is this consistent with the facts in Q#1? 42160 42162 42164 42166 42171 42173 42180 421830 1 2 3 4 5 6 Date of Onset for New Cases Number of New Cases

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