Robert P. Gage

Abstract On the basis of experience with calculated survivorships of patients following treatment for cancer, a simple function, in terms of two physically meaningful parameters, has been evolved, which fits such survivorship data very well. These two parameters can be used to compare succinctly the mortality of two groups, different in respect of treatment, type of cancer, or other characteristics. The parameters are c (“cured”), which represents the proportion of the population which is subject only to “normal” death rates, and β, which is the death rate from the cancer, to which the rest of the population [not “cured,” (1–c)] is subject. Thus if one treatment is characterized by c 1 = 0.30, β 1 = 0.25, another by c 2 = 0.20, β 2 = 0.15, this could be interpreted as meaning that while the first treatment “cured” a larger proportion of the population than did the second treatment, it did not ameliorate the deaths attributable to cancer in the patients not cured as much as did the second treatment. If l T is the proportion of the total population surviving to time t, then the function is l T = cl 0+ (1 – c)l 0e −-βt where l 0 is the net survivorship corresponding to “normal” deaths, obtained from standard life tables. A graphic method and also a “least squares” method of estimating c and β are presented with an example, and the evaluated parameters are given for several series of treated cancer patients. Expectation of life and other functions of the life table also have been calculated from the evaluated parameters, for the same series.

BACKGROUND: Outbreaks of Escherichia coli O157:H7 infections have involved direct transmission from animals and their environment to humans. We describe an outbreak among visitors to a Pennsylvania dairy and petting farm that provides public access to animals. METHODS: We conducted both a case-control study among visitors to a farm to identify risk factors for infection and a household survey to determine the rates of diarrheal illness among these visitors. We performed an extensive environmental study to identify sources of E. coli O157:H7 on the farm. RESULTS: Fifty-one patients with confirmed or suspected E. coli O157:H7 infection were enrolled in the case-control study. The median age of the patients was four years, and the hemolytic-uremic syndrome developed in eight. Contact with calves and their environment was associated with an increased risk of infection, whereas hand washing was protective. The household survey indicated that visitors to the farm during the outbreak had higher than expected rates of diarrhea. Environmental studies showed that 28 of the 216 cattle on the farm (13 percent) were colonized with E. coli O157:H7 that had the same distinct pattern on pulsed-field gel electrophoresis that was found in isolates from the patients. This organism was also recovered from surfaces that were accessible to the public. CONCLUSIONS: In a large outbreak of E. coli O157:H7 infections among visitors to a dairy farm, predominantly children, high rates of carriage of E. coli O157:H7 among calves and young cattle most likely resulted in contamination of both the animals' hides and the environment.