Mathematical modeling of epidemic syphilis transmission. Implications for syphilis control programs.

BACKGROUND AND OBJECTIVES: The past 10 years' wave of syphilis epidemics has challenged syphilis control programs. Although apparently connected to drugs-for-sex trading of crack cocaine, the genesis and resolution of these epidemics is poorly understood. GOALS OF THE STUDY: The goals of this study were to develop a mathematical model of epidemic syphilis transmission based on empiric data, to stimulate and ascertain behavioral and sociologic features necessary to produce epidemic transmission, and to explore mechanisms leading to resolution of epidemic transmission. STUDY DESIGN: The study used multi-compartment iterative computer simulation using empirically derived input data. RESULTS: Epidemic transmission resulted from adding a small core group of individuals with very high levels of partner exchange (300-400 partners per year) to a population with levels of partner exchange seen in the general population. Epidemic resolution could result from immunity or subtle changes in the size or partner exchange rate of the core group. CONCLUSION: There is a need for sexually transmitted disease control programs to reevaluate their approach to prevention and control of epidemic syphilis in light of data on transmission dynamics.

A comparison of the case-finding effectiveness and average costs of screening and partner notification.

BACKGROUND AND OBJECTIVES: Sexually transmitted disease control programs rely on case-finding through screening and partner notification to control syphilis. Difficulty in controlling recent syphilis epidemics have raised questions about the effectiveness of these strategies. GOALS OF THE STUDY: This study sought to evaluate the contributions of screening and field epidemiology to case-finding and compare average costs of these methods. STUDY DESIGN: The study was designed as a descriptive study of outcomes in a cohort tested for syphilis through a county health department. Cost-effectiveness analysis using average costs per outcome were used. RESULTS: Testing self-motivated individuals accounted for 85% of the case-finding. Testing was more cost-effective than Disease Intervention Specialist activity when measured as cost per new case. Testing and Disease Intervention Specialist activity were comparable in cost when measured in terms of a Weighted Disease Intervention Index. CONCLUSIONS: Sexually transmitted disease control programs must consider how to balance investments in screening and DIS field intervention. Programs also should reevaluate their approach to control of epidemic syphilis in light of the limited effectiveness of traditional control strategies.

A swimming-associated outbreak of hemorrhagic colitis caused by Escherichia coli O157:H7 and Shigella sonnei.

BACKGROUND: In the summer of 1991, simultaneous outbreaks of bloody diarrhea and hemolytic-uremic syndrome caused by Escherichia coli O157:H7 and of bloody diarrhea caused by Shigella sonnei were traced to a lakeside park near Portland, Oregon. METHODS: We identified cases primarily from routine surveillance reports. In case-control studies, the activities of persons with park-associated E. coli O157:H7 or S. sonnei infections were compared independently with those of three sets of controls. We also evaluated environmental conditions at the park and subtyped the bacterial isolates. RESULTS: We identified 21 persons with park-associated E. coli O157:H7 infections (all of them children; median age, six years) and 38 persons with S. sonnei infections (most of them children). These 59 people had visited the park over a 24-day period. Their illnesses were not associated with food or beverage consumption. All the case patients reported swimming, however, and in case-control studies swimming was strongly associated with both types of infection (P = 0.015 or less). The case patients were more likely than the controls to report having swallowed lake water, and they had spent more time in the lake. Numbers of enterococci indicative of substantial fecal contamination (geometric mean, > 50 per deciliter) were detected in the swimming area during some but not all of the outbreak period. Park-associated E. coli O157:H7 isolates were identical by pulsed-field gel electrophoresis and were distinguishable from other isolates in the Portland area. CONCLUSIONS: Lake water that was fecally contaminated by bathers was the most likely vehicle for the transmission of both the E. coli O157:H7 and the S. sonnei infections. The unusually prolonged outbreak suggests both the survival of these enteric organisms in lake water and a low infectious dose.

Managed outcomes: a strategy to improve the nation's health.

Current health care delivery systems in the United States have led to high cost, uneven quality, less than universal coverage, undue emphasis on a medical/clinical model, and scant attention to primary care and prevention. In the context of health care reform, a new strategy is introduced that reverses present trends and incentives, called managed outcomes. This strategy is not specific to any particular health care delivery system. Managed outcomes encourages experimentation and flexibility in the design of health care systems and fosters primary care, health promotion, and disease prevention models. It links purchasing decisions to established specific and measurable goals that can provide quality and cost-effective services to improve health.

Syphilis, sex and crack cocaine: images of risk and morality.

A new epidemic of syphilis in the Portland, Oregon metropolitan region mirrors a national trend in the United States. The epidemic is centered in urban areas, is associated with heterosexual transmission, and disproportionately affects people of color, especially African-Americans. The epidemic has been linked to sexual activity among users of crack cocaine, and particularly to the practice of trading sex and crack. Here, we report an analysis of in-depth interviews of 40 respondents, of whom 31 have used crack cocaine, 12 have experience as professional sex workers (prostitutes), and 12 are confirmed recent syphilis cases or their sexual contacts. These respondents confirm that sexual activity involving multiple anonymous partners often takes place within the context of crack cocaine use. They also describe sexual activity among more casual users of the drug. But respondents present themselves as having maintained an adherence to common American values regarding cleanliness, mortality, and sexual behavior. They speak of choosing sex partners according to whether a prospective partner 'looks clean.' This image of cleanliness goes beyond simple bodily hygiene, and into the realm of judgement about moral character. A person is more likely to be judged clean if he or she is known to come from a nice family, has a pleasant demeanor, or appears concerned about self-control. Such people are seen as fundamentally decent, and therefore less likely to have syphilis, a disease associated with deterioration, tearing down, dirtiness and disordering. Thus, respondents use conceptions of cleanliness and morality in constructing definitions of high- and low-risk sexual behavior, as they negotiate a life that endangers their sense of moral control. In doing this, they invoke beliefs and values central to the dominant culture surrounding them. This points to the limits of defining crack cocaine users, and other communities of drug users, as being culturally different from the rest of us.

Partner notification: can it control epidemic syphilis?

STUDY OBJECTIVE: During 1987, the rate of syphilis among heterosexual adults in Oregon increased 159%, yet the number of cases of gonorrhea remained stable. Our study was done to evaluate why the same control measures contained gonorrhea but not syphilis in this population. DESIGN: Exploratory case-control study. SETTING: Public health clinics in Portland, and Salem, Oregon. PATIENTS: All 146 heterosexual adults with early syphilis and all 164 heterosexual adults with acute gonorrhea reported to the public health clinics during April to July 1988. INTERVENTION: A questionnaire was administered to all syphilis case-patients and control patients (those with gonorrhea) at the beginning of the routine, sexually transmitted disease (STD), investigative interview. MEASUREMENTS AND MAIN RESULTS: Syphilis case-patients had contact with an average of 5.0 sex partners for whom they could not supply locating information sufficient to initiate partner notification. In contrast, patients with gonorrhea had contact with an average of 0.4 sex partners for whom they could not supply locating information (P less than 0.005). The 28% (41 of 146) of syphilis case-patients who reported having exchanged sex for drugs or money accounted for 72% (527 of 729) of the unlocatable partners exposed to syphilis. In contrast, the 17% (28 of 164) of patients with gonorrhea who reported having exchanged sex for drugs or money accounted for 36% (25 of 69) of the unlocatable partners exposed to gonorrhea. CONCLUSIONS: Because patients infected with syphilis have relatively large numbers of anonymous sexual encounters, prevention strategies that supplement partner notification are urgently needed to control the syphilis epidemic among adults.