The detection of unusual patterns in the occurrence of diseases and other health events presents an important challenge to public health surveillance. This paper discusses three analytic methods for identifying aberrations in underlying distributions. The methods are illustrated on selected infectious diseases included in the National Notifiable Diseases Surveillance System of the Centers for Disease Control. Results suggest the utility of such an analytic approach. Further work will determine the sensitivity of such methods to variations in the occurrence of disease. These methods are useful for evaluating and monitoring public health surveillance data.
Giardiasis is the most frequently reported diarrheal disease in northern New England. A case-control study of endemic giardiasis and environmental risk factors among residents of New Hampshire involved 273 cases from the state's 1984 disease registry and 375 controls. Giardiasis was associated with a shallow dug well as a residential water source (odds ratio [OR] = 2.4; 95% confidence interval [CI], 1.3-47.0), a recent history of drinking untreated surface water (OR = 3.4; CI, 2.1-5.5), a history of swimming in a lake or pond (OR = 4.6; CI, 2.4-86.0) or swimming in any natural body of fresh water (OR = 4.0; CI, 2.3-70.0), contact with a person thought to have giardiasis (OR = 2.3; CI, 1.4-36.0), and recent contact with a child in day care (OR = 1.5; CI, 1.0-2.1). Multivariate modeling supported these associations. Shallow wells, relatively common in New Hampshire, have not previously been established as important sources of giardiasis.
In the period July through October, 1986, 78 laboratory-confirmed cases of cryptosporidiosis were identified in New Mexico. To determine possible risk factors for development of this disease, we conducted a case-control study; 24 case-patients and 46 neighborhood controls were interviewed. Seventeen (71 per cent) of the 24 case-patients were females, seven (29%) were males; their
In the period November 1, 1985 to January 31, 1986, 703 cases of giardiasis were reported in Pittsfield, Massachusetts (population 50,265). The community obtained its water from two main reservoirs (A and B) and an auxiliary reservoir (C). Potable water was chlorinated but not filtered. The incidence of illness peaked approximately two weeks after the city began obtaining a major portion of its water from reservoir C, which had not been used for three years. The attack rate of giardiasis for residents of areas supplied by reservoir C was 14.3/1000, compared with 7.0/1000 in areas that received no water from reservoir C. A case-control study showed that persons with giardiasis were more likely to be older and
IntroductionWaterborne giardiasis is becoming an important public health problem in the United States: during the period from 1965-84, 90 outbreaks and 23,776 cases of giardiasis were reported. Sixty-nine per cent of outbreaks and 74 per cent of
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