Primary respiratory syncytial virus infection: pathology, immune response, and evaluation of vaccine challenge strains in a new mouse model

Respiratory syncytial virus (RSV) is the primary cause of lower respiratory tract illness in young children. Vaccine development has been hampered by the experience of the formalin-inactivated vaccine tested in the 1960's. Currently, several vaccine candidates are under development and immune response to these candidate vaccines must be evaluated closely. We introduce a novel low-dose murine model of RSV infection and a new pathologic scoring system for the resultant pulmonary disease. We have also developed new sensitive methods for measuring cytokine expression. We then used this new model to test vaccine challenge strains of RSV in order to determine their pathogenicity.

The Campylobacter fetus S layer is not essential for initial interaction with HEp-2 cells

In vitro adherence assays were used to determine whether the S layer mediated interactions between Campylobacter fetus subsp. venerealis strains and HEp-2 cells. At multiplicity of infection ratios ranging from 0.1:1 through 100:1, quantitation of bacterial adherence by light microscopy revealed that S layer deficient isogenic C. fetus 809K and C. fetus 810K were not less efficient in their attachment to HEp-2 cells; either S layer deficient C. fetus strains interacted with HEp-2 cells in greater numbers than the corresponding wild-type parent strains 809 and 810 or there was no significant difference in adherence levels between wild-type and mutant strains. Adherence of C. fetus strains to HEp-2 cells increased most during the first 2 h of a 22-h incubation period with only a slight increase in C. fetus cell numbers occurring subsequent to 2 h. At each assay point throughout this 22-h time period, equivalent numbers of wild-type and S layer deficient C. fetus strains were observed associated with HEp-2 cells. Prior to 2 h, adherence levels of all C. fetus strains exceeded those of Escherichia coli AB264 and Salmonella typhimurium SL1344. And, unlike S. typhimurium, C. fetus did not undergo significant replication following initial adherence to HEp-2 cells. Campylobacter fetus did not adhere to HEp-2 cells in a localized or aggregative pattern but were randomly distributed over individual HEp-2 cells and at no time during the assay with C. fetus were changes in HEp-2 cell morphology apparent. These data suggest that the S layer is not essential for mediating initial interactions between C. fetus and HEp-2 cells.

TheCampylobacter fetusS layer is not essential for initial interaction with HEp-2 cells

In vitro adherence assays were used to determine whether the S layer mediated interactions between Campylobacter fetus subsp. venerealis strains and HEp-2 cells. At multiplicity of infection ratios ranging from 0.1:1 through 100:1, quantitation of bacterial adherence by light microscopy revealed that S layer deficient isogenic C. fetus 809K and C. fetus 810K were not less efficient in their attachment to HEp-2 cells; either S layer deficient C. fetus strains interacted with HEp-2 cells in greater numbers than the corresponding wild-type parent strains 809 and 810 or there was no significant difference in adherence levels between wild-type and mutant strains. Adherence of C. fetus strains to HEp-2 cells increased most during the first 2 h of a 22-h incubation period with only a slight increase in C. fetus cell numbers occuring subsequent to 2 h. At each assay point throughout this 22-h time period, equivalent numbers of wild-type and S layer deficient C. fetus strains were observed associated with HEp-2 cells. Prior to 2 h, adherence levels of all C. fetus strains exceeded those of Escherichia coli AB264 and Salmonella typhimurium SL1344. And, unlike S. typhimurium, C. fetus did not undergo significant replication following initial adherence to HEp-2 cells. Campylobacter fetus did not adhere to HEp-2 cells in a localized or aggregative pattern but were randomly distributed over individual HEp-2 cells and at no time during the assay with C. fetus were changes in HEp-2 cell morphology apparent. These data suggest that the S layer is not essential for mediating initial interactions between C. fetus and HEp-2 cells.Key words: Campylobacter fetus, S layer, HEp-2.

Surveillance for Escherichia coli O157:H7 infections in Minnesota by molecular subtyping

BACKGROUND

Escherichia coli O157:H7 is a leading cause of diarrhea and the hemolytic-uremic syndrome. Current public health surveillance for E. coli O157:H7 requires considerable resources; traditional methods lack the sensitivity and specificity to detect outbreaks effectively.

METHODS

During 1994 and 1995, the Minnesota Department of Health requested that all clinical isolates of E. coli O157:H7 be submitted to our laboratory. Isolates were subtyped by pulsed-field gel electrophoresis (PFGE), and patients were interviewed about potential sources of infection.

RESULTS

In 1994 and 1995, 344 cases of E. coli O157:H7 infection were reported to the Minnesota Department of Health; 317 (92 percent) were subtyped by PFGE, and 143 distinct PFGE patterns were identified. Ten outbreaks of E. coli O157:H7 were identified; these accounted for 56 (18 percent) of the 317 subtyped cases. Four outbreaks were detected solely as a result of subtype-specific surveillance. In 11 two-week periods, the number of reported cases of E. coli O157:H7 doubled from the previous two weeks. In eight of these instances, the patterns identified were dissimilar and there were no outbreaks. Two of the remaining three increases resulted from multiple simultaneous outbreaks.

CONCLUSIONS

Subtype-specific surveillance for E. coli O157:H7 can identify outbreaks that are not detected by traditional methods and can ascertain whether sudden increases in reported cases are due to sporadic isolated cases or to one or more outbreaks.

A population-based study of sexually transmitted disease incidence and risk factors in human immunodeficiency virus-infected people

BACKGROUND AND OBJECTIVES

The Minnesota Department of Health conducts active surveillance for cases of human immunodeficiency virus (HIV) infection and passive surveillance for gonorrhea, Chlamydia trachomatis infection, and syphilis. The authors linked two computerized surveillance databases to assess gonorrhea incidence and risk factors for sexually transmitted disease (STD) acquisition among people with known HIV infection.

STUDY DESIGN

People diagnosed with adolescent/adult HIV infection before 1993 and still alive as of December 31, 1994 were compared to people diagnosed with gonorrhea, chlamydial infection, or primary/secondary syphilis in 1993 or 1994. Records were matched on name, date of birth, and gender. The incidence of reported gonorrhea was calculated and risk factors for STD acquisition were examined.

RESULTS

Thirty (1.3%) of 2,315 HIV-infected people were diagnosed with one or more STDs after HIV diagnosis (median interval: 3 years). There were 31 episodes of gonorrhea, seven episodes of chlamydial infection, and one episode of secondary syphilis. The gonorrhea incidence among HIV-infected people was high compared to the general population in Minnesota, even after stratifying by gender, age, and county of residence. STD acquisition was independently associated with female gender (odds ratio [OR] = 3.8; 95% confidence interval [CI] = 1.7, 8.3) and residence in Hennepin County (OR = 2.9; 95% CI = 1.2, 7.1), the most populous county in Minnesota.

CONCLUSIONS

Linkage of STD and HIV surveillance data is useful as a sentinel for high-risk sexual behavior among HIV-infected people, and it can help identify individuals who require additional interventions to prevent HIV transmission. State and local health departments should consider linking these data sources to assess trends and allocate resources.

An outbreak of invasive group A streptococcal disease associated with high carriage rates of the invasive clone among school-aged children

OBJECTIVES

To determine if a common strain of group A streptococcus was responsible for an outbreak of invasive streptococcal disease in southeastern Minnesota and to determine whether this strain was prevalent among residents of this area during the outbreak who either had streptococcal pharyngitis or were asymptomatic streptococcal carriers.

DESIGN

Pharyngeal culture survey and case-contact evaluation.

SETTING

Three adjacent counties in southeastern Minnesota defined as the outbreak area. Outbreak period, January 1 through March 31, 1995.

PATIENTS

Seven patients with invasive streptococcal infection, 1249 patients (adults and children) with sore throat who resided in the outbreak area, children from an elementary school located in 1 community where the majority of invasive cases occurred, and 896 students from 3 schools located in Minnesota counties outside the outbreak area.

MEASUREMENTS

Pulsed-field gel electrophoresis (DNA fingerprinting) of group A streptococcal isolates obtained from patients with invasive disease, throat swabs of patients with sore throat, and throat swabs of asymptomatic school-aged children.

RESULTS

All patients with outbreak-associated invasive disease had group A streptococcal isolates that were indistinguishable by pulsed-field gel electrophoresis. Additional testing showed that these isolates carried significant virulence factors including pyrogenic exotoxin A and streptococcal superantigen. Five of these 7 patients with invasive disease had underlying medical conditions; 4 developed toxic shock syndrome and died (case fatality, 57%). The outbreak-associated group A streptococcal clone was found in 69 (26.5%) of the 260 patients with sore throat from whom group A streptococcus was isolated. The frequency of the outbreak clone among pharyngeal carriers from the 3 schools outside the outbreak area was significantly less (range, 0%-10%) than in children from the school in the outbreak area (78%; relative risk, 29; 95% confidence interval, 11.1-78.1; P<.001). Four of the 7 patients with outbreak-associated disease had contact with children who attended the school in the outbreak area.

CONCLUSIONS

A single clone of group A streptococcus was responsible for 7 cases of invasive streptococcal disease during an outbreak in Minnesota and for a significant number of pharyngitis cases that also occurred during the outbreak. Invasive disease occurred most frequently in persons with underlying medical conditions. This outbreak was also associated with increased carriage rates of the invasive streptococcal clone among community school-aged children. Cases of invasive group A streptococcal infection may therefore reflect the tip of the iceberg with regard to the burden of colonization of a specific invasive streptococcal clone in a community.

Screening for tuberculosis infection among secondary school students in Minneapolis-St. Paul: policy implications

Three students in the St. Paul Public Schools were diagnosed with active tuberculosis (TB) in late 1991 and early 1992. To define the prevalence of TB infection in St. Paul and Minneapolis, we conducted school-based screening projects in the St. Paul and Minneapolis public schools during 1992 and 1993. In St. Paul, 7,596 (74.8%) students in grades six through 12 received Mantoux tests; 268 (3.5%) were reactive. Infection rates varied significantly by country of birth, with students born outside the United States more likely to be Mantoux reactors than U.S.-born students (RR = 20.2; 95% CI = 14.9-27.3; p < 0.001). In Minneapolis, 752 (47.2%) eighth-grade students received Mantoux tests; 23 (3.1%) were reactive. As in St. Paul, infection rates varied by country of birth; students born outside the United States were more likely to have reactive Mantoux tests than students born in this country (RR = 13.2; 95% CI = 5.6-31.4; p < 0.001). We conclude that routine TB screening of school students is not warranted in Minnesota, although school-based screening targeted at the highest risk students, particularly those born outside the United States, may be a beneficial prevention strategy.

A national outbreak of Salmonella enteritidis infections from ice cream. The Investigation Team

BACKGROUND

In September 1994, the Minnesota Department of Health detected an increase in the number of reports of Salmonella enteritidis infections. After a case-control study implicated a nationally distributed brand of ice cream (Schwan's) in the outbreak, the product was recalled and further epidemiologic and microbiologic investigations were conducted.

METHODS

We defined an outbreak-associated case of S. enteritidis infection as one in which S. enteritidis was cultured from a person who became ill in September or October 1994. We established national surveillance and surveyed customers of the implicated manufacturer. The steps involved in the manufacture of ice cream associated with cases of S. enteritidis infection were compared with those of products not known to be associated with infection matched for the date of manufacture. Cultures for bacteria were obtained from ice cream samples, the ice cream plant, and tanker trailers that had transported the ice cream base (premix) to the plant.

RESULTS

We estimate that S. enteritidis gastroenteritis developed in 224,000 persons in the United States after they ate Schwan's ice cream. The attack rate for consumers was 6.6 percent. Ice cream associated with infection contained a higher percentage of premix that had been transported by tanker that had carried nonpasteurized eggs immediately before (P = 0.02). S. enteritidis was isolated from 8 of 226 ice cream products (3 percent), but not from environmental samples obtained from the ice cream plant (n = 157) or tanker trailers (n = 204).

CONCLUSIONS

This nationwide outbreak of salmonellosis was most likely the result of contamination of pasteurized ice cream premix during transport in tanker trailers that had previously carried nonpasteurized liquid eggs containing S. enteritidis. To prevent further outbreaks, food products not destined for repasteurization should be transported in dedicated containers.

A case-control study to assess possible triggers and cofactors in chronic fatigue syndrome

PURPOSE

To assess possible triggers and cofactors for chronic fatigue syndrome (CFS) and to compare levels of selected cytokines between cases and an appropriately matched control group.

PATIENTS AND METHODS

We conducted a case-control study of 47 cases of CFS obtained through a regional CFS research program maintained at a tertiary care medical center. One age-, gender-, and neighborhood-matched control was identified for each case through systematic community telephone sampling. Standardized questionnaires were administered to cases and controls. Sera were assayed for transforming growth factor-beta (TGF-beta), interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha, and antibody to Borrelia burgdorferi and Babesia microti.

RESULTS

Cases were more likely to have exercised regularly before illness onset than controls (67% versus 40%; matched odds ratio (MOR) = 3.4; 95% CI = 1.2 to 11.8; P = 0.02). Female cases were more likely to be nulliparous prior to onset of CFS than controls (51% versus 31%; MOR = 8.0; 95% CI = 1.03 to 170; P = 0.05). History of other major factors, including silicone-gel breast implants (one female case and one female control), pre-morbid history of depression (15% of cases, 11% of controls) and history of allergies (66% of cases, 51% of controls) were similar for cases and controls. However, cases were more likely to have a diagnosis of depression subsequent to their diagnosis of CFS compared to a similar time frame for controls (MOR = undefined; 95% CI lower bound = 2.5; P < 0.001). Positive antibody titers to B burgdorferi (one case and one control) and B microti (zero cases and two controls) were also similar.

CONCLUSIONS

Further investigation into the role of prior routine exercise as a cofactor for CFS is warranted. This study supports the concurrence of CFS and depression, although pre-morbid history of depression was similar for both groups.

Statewide survey of laboratories performing Mycobacterium tuberculosis testing in Minnesota

Rapid and accurate laboratory detection and identification of Mycobacterium tuberculosis, particularly multidrug-resistant strains, is critical to both public health control measures and patient management. The authors surveyed microbiology laboratories to evaluate whether their methods met national guidelines. As needed, laboratories received individualized recommendations for improvement. The laboratories were resurveyed a year later to assess changes in methods. Current guidelines recommend fluorochrome acid-fast smears, broth cultures, identification by nucleic acid probe or BACTEC-NAP, and BACTEC primary susceptibility panels, which should include pyrazinamide. Of 27 laboratories performing acid-fast smears, 15 used fluorochrome methods. Six of 16 laboratories performing mycobacterial cultures used broth media. Of six laboratories performing species identification, five used nucleic acid probes or BACTEC-NAP. Of five laboratories evaluating drug sensitivity, two used BACTEC and two included pyrazinamide in their protocols. Overall, 24 (89%) laboratories needed improvements; a year later, 16 (67%) of those had altered their methods or made definite plans to do so. Survey results suggest that health departments can facilitate improvements in laboratory testing for pathogens of public health importance.

An outbreak of measles at an international sporting event with airborne transmission in a domed stadium

An outbreak of measles occurred in conjunction with the International Special Olympics Games in the Minneapolis-St. Paul metropolitan area during July 1991. Sixteen outbreak-associated cases of measles were reported among US residents from seven states, with 9 additional cases resulting from subsequent transmission. The primary case was a track and field athlete from Argentina. Transmission occurred in three settings: the opening ceremonies in a domed stadium, track and field events, and first aid stations. Eight secondary cases had their only potential exposure at the opening ceremonies; 2 of these cases were unrelated spectators sitting in the same section of the upper deck > 30.5 m above the athlete's entrance. These findings demonstrate that the risk of indigenous measles transmission associated with international events in the United States must be considered, even in areas without recent measles activity. Moreover, the dynamic airborne transmission of measles illustrates the potential for transmission in the absence of a recognized exposure.

Physician attitudes and practices regarding universal infant vaccination against hepatitis B infection in Minnesota: implications for public health policy

Physician attitudes and practices regarding universal infant vaccination against hepatitis B virus infection in Minnesota were assessed approximately 1 year after publication of the Immunization Practices Advisory Committee recommendations. Four-hundred eighteen Minnesota family physicians and pediatricians were sent self-administered questionnaires, with follow-up by telephone. Among physicians who provide care to infants, 67 (29%) of 234 family physicians and 29 (50%) of 58 pediatricians routinely offered hepatitis B vaccine to all infants (overall 33%) (P = 0.002). The recommendations of the Immunization Practices Advisory Committee, the American Academy of Pediatrics and the American Academy of Family Physicians had the greatest positive influence on physicians' opinions regarding routine hepatitis B vaccination. The factors with the greatest negative influence on their opinions were the low prevalence of hepatitis B virus infection in Minnesota and the addition of three injections to the current childhood immunization schedule. Universal infant hepatitis B vaccination remains controversial among Minnesota family physicians and pediatricians. We believe, given the variability in hepatitis B virus incidence and prevalence in the United States and the relatively low risk of most infants, that a single national policy based solely on universal infant immunization may be difficult to implement.

Evaluation of clinical and laboratory aspects of antibody tests for detection of hepatitis C virus infection in blood donors and recipients from a low-risk population

BACKGROUND

When the first-generation enzyme immunoassay (EIA) for detection of antibody to hepatitis C virus (anti-HCV) was approved in May 1990, blood banking agencies recommended testing of all components in inventory. In many cases, one or more components from these units had already been transfused.

STUDY DESIGN AND METHODS

Donors that reacted in first-generation EIAs and recipients of their components were identified, and anti-HCV test methods (including first-generation EIA, second-generation EIA, and recombinant immunoblot assay [RIBA]) were evaluated.

RESULTS

Of 66 donors identified as anti-HCV-positive by first-generation EIA, 17 were positive in second-generation EIA. Of these 17, 9 reacted in RIBA; 6 of these showed evidence of HCV infection in polymerase chain reaction (4) and/or probable transmission of HCV to a transfusion recipient (3). Of the 48 specimens that were positive in first-generation EIA and negative in second-generation EIA, only 1 was positive in RIBA; serum was not available for polymerase chain reaction testing, and there were no living transfusion recipients in whom to assess evidence of transmission of HCV.

CONCLUSION

This study documents the low predictive value of EIAs for anti-HCV in a low-prevalence blood donor population and emphasizes the need for additional testing to confirm the specificity of samples that react in the screening tests.

Factors associated with the geographic variation of reported Chlamydia infection in Minnesota

BACKGROUND AND OBJECTIVES

In Minnesota, physicians have been required to report cases of Chlamydia trachomatis infection since 1985. The distribution of reported cases suggests that there is substantial geographic variation in the rate of chlamydia infection.

GOAL OF THIS STUDY

We conducted chlamydia screening at selected sites and a survey of primary care physicians in counties with high and low rates of reported chlamydia infection. We hypothesized that chlamydia infections are uniformly distributed in nonmetropolitan areas, and the geographic differences in reported cases can be attributed to variable testing and reporting practices by physicians.

STUDY DESIGN

The number of reported female chlamydia cases per 1,000 women was calculated for each rural Minnesota county in 1990. Fourteen counties with high and low rates of reporting were selected for further investigation. From September to December 1991, universal chlamydia screening was carried out at 11 clinics serving patients in these counties. A questionnaire was mailed to all primary care physicians in these counties.

RESULTS

In 1990, the rate of reported chlamydia cases was 4.7/100,000 and 0.1/100,000 for women living in the high-reporting and low-reporting counties, respectively. Chlamydia infection was present in 5.5% and 9.7% of women screened at selected clinics in high- and low-reporting counties, respectively. Physicians in high- and low-reporting counties did not differ significantly in terms of age, gender, number of pelvic exams, or frequency of chlamydia testing. However, physicians in high-reporting counties were significantly more likely to test for chlamydia when evaluating mucopurulent cervicitis or salpingitis, and they were more likely to test a woman whose sex partner had urethritis. Physicians in high-reporting counties were also more likely to have reported a case of chlamydia.

Risk factors for lack of detectable antibody following hepatitis B vaccination of Minnesota health care workers

OBJECTIVE

To assess the presence of antibody to hepatitis B surface antigen (anti-HBs) at postvaccination testing in Minnesota health care workers receiving recombinant hepatitis B vaccines, and to identify risk factors for lacking anti-HBs following hepatitis B vaccination.

DESIGN

Retrospective cohort study.

SETTING

Ten acute care hospitals in Minnesota.

PARTICIPANTS

A total of 595 health care workers who had received hepatitis B vaccine (Recombivax HB or Engerix-B) between June 1987 and December 1991 and who underwent postvaccination testing for anti-HBs within 6 months after receiving the third dose of vaccine.

MAIN OUTCOME MEASURE

Presence or absence of anti-HBs following hepatitis B vaccination.

RESULTS

Five variables were independently associated with lacking anti-HBs by multivariate analysis: vaccine brand, smoking status, gender, age, and body mass index. Stratifying by vaccine brand demonstrated that age (P = .01), body mass index (P < .01), and smoking status (P < .01) were associated with lacking anti-HBs only for Recombivax HB recipients; and gender (P = .03) was associated with lacking anti-HBs only for Engerix-B recipients. After controlling for smoking status, age, gender, and body mass index, recipients of Recombivax HB were more likely to lack anti-HBs than recipients of Engerix-B (relative risk, 2.3; 95% confidence interval, 1.1 to 4.7; P = .02).

CONCLUSIONS

Results indicate that certain populations of health care workers are at increased risk of not responding to hepatitis B vaccination. Further studies evaluating immunogenicity of currently available recombinant hepatitis B vaccines in persons at high risk for primary vaccine failure are needed.

Pathogen-specific risk factors and protective factors for acute diarrheal disease in urban Brazilian infants

To evaluate potential risk factors and protective factors for acute diarrheal disease in urban infants, 500 infants < or = 12 months old with diarrhea and 500 age-matched control subjects coming to a São Paulo emergency room were studied. On multivariate analysis, these apparently sporadic community-acquired cases of diarrhea were significantly associated with hospitalization in the month before onset (odds ratio [OR], 3.4), day care center exposure (OR, 2.0), prior diarrhea in another household member (OR, 4.4), and low family income (OR, 1.8). Breast-feeding infants < 6 months old (OR, 0.3) and boiling household drinking water (OR, 0.4) were protective. Enteropathogenic Escherichia coli (EPEC; OR, 12.0) and Salmonella (OR, 7/0, discordant pairs) infections were associated with prior hospitalization, rotavirus infections were associated with day care (OR, 6/0), and breast-feeding was protective against EPEC infections (OR, 0.1). These results suggest that certain preventive strategies can prevent a substantial proportion of cases of diarrheal disease in Brazilian infants.

Transmission of Escherichia coli O157:H7 infection in Minnesota child day-care facilities

OBJECTIVE

Escherichia coli O157:H7 infection can cause hemorrhagic colitis and hemolytic uremic syndrome. Since 1988 the Minnesota Department of Health has carried out surveillance for this infection. To assess the occurrence of person-to-person transmission within day-care facilities, we investigated facilities where an infected child attended after onset of symptoms.

DESIGN

Parents of children less than 5 years old with E coli O157:H7 infection were interviewed from July 1988 through December 1989. If the child attended day care after onset, stool cultures were obtained from other children in attendance and their parents were interviewed. If there was presumptive evidence of ongoing E coli O157:H7 transmission in a facility, all preschool children were excluded from attending day-care facilities until two consecutive stool cultures were negative.

RESULTS

Sixty-eight cases of E coli O157:H7 infection were identified in Minnesota during the 18-month period, including 29 cases identified through investigations at nine day-care facilities. There was evidence of person-to-person transmission in all nine facilities. The median number of infected children per facility was two (range, two to 18), and the median attack rate was 22% (range, 3% to 38%). The median age of the primary case at each facility was 26 months (range, 12 to 59 months). There was no evidence of further transmission at facilities where children were temporarily excluded until two consecutive stool cultures were negative.

CONCLUSION

Person-to-person transmission of E coli O157:H7 is common when infected preschool children attend day care while symptomatic. The number of unrecognized day-care outbreaks in the United States may be substantial due to the lack of routine testing for this pathogen in stool cultures, the absence of public health surveillance in many regions, and incomplete follow-up of infected children. Temporary exclusion of all children was an effective control strategy in this population, but additional investigations are needed to determine the optimal intervention.

Role of egg consumption in sporadic Salmonella enteritidis and Salmonella typhimurium infections in Minnesota

The incidence of Salmonella enteritidis infections has increased in the eastern United States, and consumption of undercooked eggs has been associated with outbreaks of S. enteritidis. In Minnesota, the incidence of S. enteritidis infections doubled from 1980 to 1990; however, no egg-associated outbreaks were identified. A case-control study was conducted to examine potential exposures for S. enteritidis and Salmonella typhimurium infections in Minnesota adults. Sporadic cases of S. enteritidis (odds ratio [OR], 5.2; 95% confidence interval [CI], 1.9-14.2; P = .003) and S. typhimurium infection (OR, 2.4; CI, 1.1-5.5; P = .03) were more likely to have consumed undercooked eggs or egg-containing foods during the 3 days before onset of illness compared to a similar reference period for controls. In addition, the extent to which eggs were cooked was directly associated with illness (chi 2 test for trend, P < .001). These findings demonstrate that eggs are important vehicles for S. enteritidis and S. typhimurium, even in the absence of recognized outbreaks.

Campylobacter enteritis outbreaks associated with drinking raw milk during youth activities. A 10-year review of outbreaks in the United States

OBJECTIVE

To determine the incidence of recognized outbreaks of Campylobacter enteritis associated with drinking raw milk during youth activities.

DESIGN

Retrospective survey of 51 state and territorial health departments.

SETTING

The 50 United States and the Territory of Puerto Rico.

POPULATIONS

Persons in preschool through college.

MEASUREMENT

Information was obtained for all Campylobacter outbreaks associated with consumption of raw milk during youth activities from 1981 through 1990 that were investigated by state and territorial health departments.

RESULTS

Twenty outbreaks were identified in 11 states. Four hundred fifty-eight outbreak-associated cases occurred among 1013 persons who drank raw milk, with an overall attack rate of 45%. At least one outbreak was reported for each year of the 10-year period. Fourteen outbreaks (70%) occurred among children in kindergarten through third grade, compared with one outbreak (5%) among fourth through sixth graders. The remaining five outbreaks (25%) occurred in mixed groups of children and teenagers. Only nine (60%) of 15 outbreaks identified from 1981 through 1988 were reported to the Campylobacter national surveillance system maintained by the Centers for Disease Control and Prevention.

CONCLUSION

Drinking raw milk on school field trips or other youth activities continues despite the occurrence of multiple Campylobacter outbreaks documented from this practice. Such illnesses can be prevented by educating dairy farmers and officials of schools and youth organizations about the hazards of drinking raw milk. Public health organizations need to develop and implement such educational programs.

A multistate outbreak of Salmonella javiana and Salmonella oranienburg infections due to consumption of contaminated cheese

OBJECTIVE

To determine the source of an outbreak of Salmonella javiana and Salmonella oranienburg infections.

DESIGN

Laboratory-based statewide surveillance for Salmonella infections and two separate case-control studies.

SETTING

Community- and industry-based studies conducted from May through October 1989.

PARTICIPANTS

Thirty-one culture-confirmed outbreak-associated cases of S javiana infection and 60 community controls matched for telephone prefix, gender, and age in case-control study I; 50 cases, 100 community controls, and 64 family member controls in case-control study II.

RESULTS

One hundred thirty-six culture-confirmed cases of S javiana infection and 11 cases of S oranienburg infection were associated with the outbreak in Minnesota. Outbreak-associated cases were also identified in Wisconsin (15 cases), and in Michigan and New York (one case each). Cases were more likely than controls to have consumed mozzarella cheese manufactured at a single cheese plant (plant X) or cheese that had been shredded at processing plants that also shredded cheese manufactured at plant X (odds ratio [OR], 7.2; 95% confidence interval [CI], 1.7 to 23.2; P < .01). The outbreak-associated strains of both serovars were isolated from two unopened 16-oz (0.45-kg) blocks of mozzarella cheese produced at plant X. The most probable numbers of Salmonella organisms in these samples were 0.36/100 g and 4.3/100 g.

CONCLUSIONS

The potential for bacterial pathogen contamination of cheese during manufacture and processing has important epidemiologic implications, particularly because cheese consumption has recently increased in the United States. Low-level contamination of a nationally distributed food product can cause geographically dispersed foodborne outbreaks that may be difficult to detect.

An outbreak of Salmonella enteritidis infection at a fast-food restaurant: implications for foodhandler-associated transmission

An outbreak of Salmonella enteritidis infection occurred in patrons and employees of a fast-food restaurant. Transmission took place over a 9-day period. A single employee (employee A) was identified who had onset of gastrointestinal illness 1 day before the first reported patron exposures and had S. enteritidis isolated from stool. A case-control study of 37 ill and 20 healthy patrons who ate during shifts worked by employee A demonstrated that curly-fried potatoes and ice (odds ratio [OR], 6.8; 95% confidence interval [CI], 1.5-33.7; P = .007), both food items handled bare-handed by employee A, were associated with illness. Employees who worked two or more shifts with employee A were more likely to be infected than those who did not work with employee A (OR, 4.4; CI, 1.0-19.5; P = .03). Foodhandlers who subsequently became infected apparently contaminated multiple food items with additional transmission to patrons. This outbreak illustrates the potential for foodhandlers in a fast-food restaurant setting who are infected with Salmonella to be a source of transmission.

A look-back investigation of patients of an HIV-infected physician. Public health implications

BACKGROUND

Transmission of the human immunodeficiency virus (HIV) to five patients receiving care from an HIV-infected dentist in Florida has recently been reported. Current data indicate that the risk of HIV transmission from health care workers to patients is low. Despite this low risk, programs to notify patients of past exposure to an HIV-infected health care worker are being conducted with increasing frequency.

METHODS

We recently conducted an investigation of all the patients cared for by an HIV-infected family physician during a period when he had severe dermatitis caused by Mycobacterium marinum on his hands and forearms. After reviewing the patients' records, we notified 336 patients who had undergone one or more procedures (digital examination of a body cavity or vaginal delivery) placing them at potentially increased risk of HIV infection. The patients were offered tests for HIV infection and counseling.

RESULTS

Of the 336 patients, 325 (97 percent) had negative tests for HIV antibody, 3 (1 percent) refused testing, 1 (less than 1 percent) died of a cause unrelated to HIV infection before notification, and the HIV-antibody status of 7 (2 percent) remained unknown. The direct and indirect public health costs of this investigation were approximately $130,000.

CONCLUSIONS

The results of this investigation raise important questions about the risk of HIV transmission from health care workers to patients and the usefulness of HIV look-back programs, particularly in the light of recently published recommendations from the Centers for Disease Control. We propose that before a look-back investigation is undertaken, there should be a clearly identifiable risk of transmission of the infection, substantially higher than the risk requiring limitation of an HIV-infected health care worker's practice prospectively.

An outbreak of Escherichia coli O157:H7 colitis associated with consumption of precooked meat patties

An outbreak of Escherichia coli O157:H7 hemorrhagic colitis at a Minnesota junior high school in October 1988 comprised 32 cases among 1562 students (attack rate, 2.0%). Four children were hospitalized; none developed hemolytic-uremic syndrome. Case children were more likely than controls to have eaten heat-processed meat patties (odds ratio, 6.2; 95% confidence interval, 2.0-20.1; P less than .001) in the school cafeteria on a specific day. The minimum estimated attack rate among students who ate these patties was 8%. The patties should have been sufficiently cooked by the manufacturer to destroy enteric pathogens before they were frozen and distributed. E. coli were cultured from frozen patties that were manufactured at the same plant on the same dates as the implicated patties, but serotype O157:H7 was not isolated. Heat-processed meat patties may serve as vehicles for E. coli O157:H7 infection, and currently there are no federal or state regulatory standards to ensure the safety of these products.

Enteropathogens associated with acute diarrheal disease in urban infants in São Paulo, Brazil

To determine the prevalence and epidemiology of enteropathogens in acute infantile diarrhea, 500 infants less than or equal to 12 months of age with diarrhea and 500 age-matched control subjects coming to a São Paulo emergency room were studied. Enteropathogens were identified in 55% of case infants and 10% of controls; enteropathogenic Escherichia coli (EPEC) of classic EPEC serotypes producing EPEC adherence factor (EAF) (26% of case infants), rotavirus (14%), Salmonella species (8%), enterotoxigenic E. coli (7%), and Shigella species (5%) were associated with diarrhea. Isolation of EAF+ classic EPEC decreased with increasing age of cases and peaked in spring, whereas rotavirus was least common in early infancy and peaked in fall and winter. Bloody stool had a 36% positive predictive value for Shigella infection, EAF+ classic EPEC were highly resistant to antimicrobial drugs. Among poor São Paulo infants, EAF+ classic EPEC equaled or exceeded rotavirus throughout the year as a cause of diarrhea bringing children to medical attention.

The epidemiology and clinical aspects of the hemolytic uremic syndrome in Minnesota

BACKGROUND

The frequency of the hemolytic uremic syndrome, characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal failure, is increasing. Although Escherichia coli serotype O157:H7 has been implicated as a causative agent, more information is needed about the basic epidemiology and clinical aspects of this syndrome.

METHODS

We conducted a retrospective population-based study of hemolytic uremic syndrome in Minnesota residents less than 18 years of age from 1979 through 1988 to assess trends in disease occurrence, describe the clinical illness, and identify predictors of disease severity and outcome. We also conducted a case-control study of patients with onsets of illness from 1986 through 1988 to examine risk factors.

RESULTS

One hundred seventeen patients were identified. The mean annual incidence increased from 0.5 case per 100,000 child-years among children less than 18 in 1979 (6 cases) to 2.0 cases per 100,000 in 1988 (26 cases) (P = 0.000004). E. coli O157:H7 was isolated from 13 of 28 patients (46 percent) who had stool specimens submitted for testing. For those who presented with typical hemolytic uremic syndrome, an elevated polymorphonuclear-leukocyte count on hospital admission, a shorter duration of prodrome, and the presence of bloody diarrhea were predictive of severe disease. In the case-control study, the patients were more likely to attend large daycare centers (more than 50 children) than were the controls (odds ratio, 10.2; P = 0.03), suggesting that day-care attendance may be a risk factor. On the basis of the population-attributable risk, however, this factor could account for no more than 16 percent of the cases.

CONCLUSIONS

This study provides evidence for an increase in the incidence of hemolytic uremic syndrome, which is probably related to an increased incidence of E. coli O157:H7 infections. Hemolytic uremic syndrome has become an important pediatric and public health problem.

Drownings in Minnesota, 1980-85: a population-based study

We conducted a population-based study of drownings in Minnesota from 1980 through 1985. Five hundred and forty-one drownings (2.1 per 100,000 person-years) were identified from death certificates and from incident reports filed with the Minnesota Department of Natural Resources. Most drownings (334, 62 percent) occurred during summer months (May-August) and involved boating (42 percent) and swimming (35 percent) events. However, 62 drownings (11 percent) occurred during winter months (December-February) and primarily involved snowmobiles and motor vehicles (71 percent) breaking through ice on lakes and waterways. The risk of drowning, estimated by the ratio of drownings to number of water-related activities, was highest during March and April, when the ice on lakes and waterway surfaces is melting, and during October and November, when lake and waterway surfaces are starting to freeze. Drowning rates were highest for males (3.7 per 100,000 person-years), persons 15 to 25 years of age (3.3 per 100,000 person-years), and children less than 5 years of age (2.5 per 100,000 person-years). These data can be used to target prevention strategies, particularly in northern climates.

An investigation of the cause of the eosinophilia-myalgia syndrome associated with tryptophan use

BACKGROUND

The eosinophilia-myalgia syndrome is a newly recognized illness that has been associated with the consumption of tryptophan products. It is not known whether the cause is related to the tryptophan itself or to chemical constituents introduced by the manufacturing process.

METHODS

To describe the epidemiology of the eosinophilia-myalgia syndrome further and elucidate a possible association with the manufacturing process, we conducted surveillance for the syndrome in Minnesota, a community survey of tryptophan use in Minneapolis-St. Paul, and a case-control study to assess potential risk factors, including the use of tryptophan from different manufacturers. We performed high-performance liquid chromatography on tryptophan samples to identify other chemical constituents.

RESULTS

The prevalence of tryptophan use increased from 1980 to 1989 and was highest among women. Among the subjects for whom the source of the tryptophan was known, 29 of 30 case patients (97 percent) and 21 of 35 controls (60 percent) had consumed tryptophan manufactured by a single company (odds ratio, 19.3; 95 percent confidence interval, 2.5 to 844.9; P less than 0.001). This company used a fermentation process involving Bacillus amyloliquefaciens to manufacture tryptophan. Analysis of the manufacturing conditions according to the retail lot demonstrated an association between lots used by case patients and the use of reduced quantities of powdered carbon in a purification step (odds ratio, 9.0; 95 percent confidence interval, 1.1 to 84.6; P = 0.014), as well as the use of a new strain of B. amyloliquefaciens (Strain V) (odds ratio, 6.0; 95 percent confidence interval, 0.8 to 51.8; P = 0.04). There was a significant correlation (r = 0.78, P less than 0.001) between the reduced amount of powdered carbon used during manufacturing and the use of the new bacterial strain. High-performance liquid chromatography of this company's tryptophan demonstrated one absorbance peak (peak E) that was present in 9 of the 12 retail lots (75 percent) used by patients and 3 of 11 lots (27 percent) used by controls (odds ratio, 8.0; 95 percent confidence interval, 0.9 to 76.6; P = 0.022).

CONCLUSIONS

The outbreak of the eosinophilia-myalgia syndrome in 1989 resulted from the ingestion of a chemical constituent that was associated with specific tryptophan-manufacturing conditions at one company. The chemical constituent represented by peak E may contribute to the pathogenesis of the eosinophilia-myalgia syndrome, or it may be a surrogate for another chemical that induces the syndrome.

Outbreak of erythromycin-resistant staphylococcal conjunctivitis in a newborn nursery

We investigated an outbreak of erythromycin-resistant Staphylococcus aureus conjunctivitis in a hospital newborn nursery that used erythromycin eye ointment to prevent ophthalmia neonatorum. Cases occurred in 2 clusters; 20 (14%) of 146 infants in the nursery developed conjunctivitis from July through October, 1987; and 5 (7%) of 69 infants in the nursery developed conjunctivitis during April and May, 1988. A case-control study of the first cluster demonstrated that culture-confirmed cases were more likely than controls to have received prophylactic erythromycin eye ointment or their initial bath from one nurse (odds ratio, 9.0; P = 0.01) or to have been delivered by one physician (odds ratio, 12.7; P = 0.03). The nurse was the only staff person to have a nasopharyngeal culture which yielded erythromycin-resistant S. aureus. Control measures, instituted in October, 1987, included using silver nitrate drops instead of erythromycin eye ointment for prophylaxis; however, in January, 1988, the hospital resumed use of erythromycin eye ointment. No additional cases were identified until mid-April, 1988, when the second cluster of cases occurred. At that time the hospital reinstituted the use of silver nitrate and no additional cases were identified. This investigation illustrates the potential for conjunctival infection with an antimicrobial-resistant pathogen when antimicrobials are used to prevent ophthalmia neonatorum.

HIV-1 counseling and testing sites, Minnesota: analysis of trends in client characteristics

We report here a summary of the data obtained from two HIV-1 antibody counseling and testing sites in Minneapolis-St. Paul for the first 48 months of operation (24,911 persons tested). The HIV-1 antibody seroprevalence rate for all persons tested was 5 percent. The highest seroprevalence rates were in male homosexual/bisexual intravenous drug users (23 percent) and homosexual/bisexual men (13 percent). There was a significant decrease in the HIV-1 antibody seroprevalence rate among clients during the 48-month period from 14 percent in the first six months to 3 percent in the last six months. This decrease coincided with an increase in the number of low-risk female clients and low-risk heterosexual male clients, and a decrease in the number of homosexual/bisexual males participating in the programs. These findings suggest the need for development and implementation of other strategies to identify and reach persons at highest risk for HIV-1 infection.

Absence of HIV infection in blood donors with indeterminate western blot tests for antibody to HIV-1

To determine whether apparently healthy persons who have had repeatedly reactive enzyme immunoassays and an indeterminate Western blot assay for antibody to the human immunodeficiency virus type 1 (HIV-1) are infected with HIV-1 or HIV-2, we studied 99 such volunteer blood donors in a low-risk area of the country. The subjects were interviewed about HIV risk factors. Coded blood specimens were tested again for HIV-1 antibody (by two different enzyme immunoassays, a Western blot assay and a radioimmunoprecipitation assay) and for HIV-2 antibody by enzyme immunoassay, for HIV-1 by the serum antigen test, for HIV-1 by culture, for human T-cell leukemia virus Type I or II antibody by enzyme immunoassay, and for sequences of HIV DNA by the polymerase chain reaction. Of the 99 blood donors, 98 reported no risk factors for HIV-1 infection; 1 donor had used intravenous drugs. After a median of 14 months (range, 1 to 30) from the time of the initial test, 65 subjects (66 percent) were still repeatedly reactive for HIV-1 antibody on at least one immunoassay. In 91 subjects (92 percent) the Western blot results were still indeterminate, whereas in 8 they were negative. No donor met the criteria for a positive Western blot assay for HIV-1, and none had evidence of HIV-1 or HIV-2 infection on culture or by any other test. We conclude that persons at low risk for HIV infection who have persistent indeterminate HIV-1 Western blots are rarely if ever infected with HIV-1 or HIV-2.

Evaluation of a sick child day care program: lack of detected increased risk of subsequent infections

A day care center for the short term care of mildly ill children opened in Minneapolis in October, 1985. We conducted a prospective study to evaluate the risk for study participants of acquiring subsequent infections as a result of possible exposure to other infectious agents while at the center. Between June, 1986, and August, 1987, we determined the rates of subsequent infections for 118 children attending the day care center (center-based children) and compared them with rates of subsequent infections for children participating in a home-based sick child care program (home-based children). Of 105 center-based children potentially exposed to respiratory illness while at the center, 24 (23%) developed subsequent respiratory illness compared with 17 (16%) of the matched home-based children (odds ratio, 1.5; 95% confidence interval, 0.7, 3.1). Of 17 center-based children potentially exposed to gastrointestinal illness, 1 (6%) developed subsequent gastrointestinal illness compared with one (6%) of the matched home-based children (odds ratio, 1.0; 95% confidence interval, 0.06, 16.0). Of 12 pairs of children, where the center-based child was potentially exposed to chickenpox while at the center and both were susceptible to chickenpox, 1 center-based child (8%) developed chickenpox compared with 2 home-based children (17%) (odds ratio, 0.5; 95% confidence interval, 0.04, 5.5). We were not able to demonstrate that children who attended the sick child day care center were at significantly increased risk of developing subsequent infections when compared with a matched group of children who did not attend the center.

An outbreak of nitrogen dioxide-induced respiratory illness among ice hockey players

During February 1987 an outbreak of nitrogen dioxide-induced respiratory illness occurred among players and spectators of two high school hockey games played at an indoor ice arena in Minnesota. The source of the nitrogen dioxide was the malfunctioning engine of the ice resurfacer. Case patients experienced acute onset of cough, hemoptysis, and/or dyspnea during, or within 48 hours of attending, a hockey game. One hundred sixteen cases were identified among hockey players, cheerleaders, and band members who attended the two games. Members of two hockey teams had spirometry performed at 10 days and 2 months after exposure; no significant compromise in lung function was documented. Nitrogen dioxide exposure in indoor ice arenas may be more common than currently is recognized; only three states require routine monitoring of air quality in ice arenas, and the respiratory symptoms caused by exposure to nitrogen dioxide are nonspecific and easily misdiagnosed.

An outbreak of psittacosis in Minnesota turkey industry workers: implications for modes of transmission and control

From June through November 1986, an outbreak of psittacosis occurred in turkey industry workers in central Minnesota. A total of 186 suspect cases were identified, and 122 cases (66%) were serologically confirmed. Cases occurred in three turkey processing plants, two rendering plants, one farm, and one "further processing" plant (where meat is removed from previously eviscerated carcasses and consumer products, such as roasts, are made). As in previous outbreaks, workers exposed to the viscera of infected birds were at greatest risk of becoming infected. However, our data showed that 31 (25%) of the confirmed cases occurred in workers at the further processing plant who had contact only with previously eviscerated carcasses. Although the specific source of infection and the mode of transmission in these workers are unclear, the use of gloves and masks by all processing workers during an outbreak might help to limit exposure. Control measures, which focused on identifying and treating ill turkey flocks, were initiated in early September; however, cases continued to occur in turkey industry workers through November. One of the flocks suspected of causing illness appeared healthy and, therefore, was not treated. Chlamydia psittaci infection in this flock was confirmed by culture after the flock had been processed. A rapid test for diagnosing C. psittaci infection in turkey flocks at the time of processing might be useful in preventing exposure of large numbers of workers.

An outbreak of giardiasis in a nursing home with evidence for multiple modes of transmission

During a 6-w period from 20 April through 7 June 1986, an outbreak of giardiasis occurred in residents and employees of a nursing home and children participating in day care at the nursing home. Eighty-eight cases of giardiasis (defined by presence of clinical symptoms or results of stool examination) were identified from groups associated with the nursing home including 35 in nursing home residents, 15 in children in day care, and 38 in employees (including kitchen staff and child care providers). Multiple modes of transmission of Giardia lamblia, including food-borne and person-to-person transmission, occurred for these groups. Evidence of transmission by food included a significant association between sandwich consumption and illness in nursing home staff (P = .04) and a significant lack of illness among nursing home residents who consumed only a pureed diet (P = .007), where all food items are cooked before serving. The primary case among the food handlers, whose illness began in mid-April, had an infected child in the day care center. Person-to-person transmission is supported by a significant association between illness and physical contact with children from the day care facility through an "adopted grandparent" program (P = .03). This is the first reported outbreak of giardiasis in a nursing home, and these findings have implications for disease control in other facilities that combine child day care and care of the elderly.

Risk factors for infant botulism in the United States

To define risk factors for infant botulism, we performed a 2-year prospective case-control study of 68 laboratory-confirmed cases in infants living in the United States, outside of California. For each case patient, two control subjects were matched by date and hospital of birth or county birth records. By univariate analysis, breast-feeding (odds ratio = 2.9) and consumption of honey (odds ratio = 9.8) were associated with disease, but only 11 case patients (16%) had eaten honey. Decreased frequency of bowel movement (less than one per day for at least 2 months) was also associated with disease in infants 2 months of age and older (odds ratio = 5.2). Risk factors changed with the age of the patient at disease onset when analyzed by multivariate logistic regression methods. For infants less than 2 months old, living in a rural area or on a farm was the only significant risk factor (odds ratio = 6.4). For infants 2 months of age and older, breast-feeding (odds ratio = 3.8), less than one bowel movement per day for at least 2 months (odds ratio = 2.9), and ingestion of corn syrup (odds ratio = 5.2) were associated with disease. The severity of the disease was similar for breast- and bottle-fed infants. Clearly defined food exposures account for a minority of infant botulism cases. Preexisting host factors, such as intestinal flora and frequency of bowel movements, may be the most important risk factors for development of disease.

Performance characteristics of serologic tests for human immunodeficiency virus type 1 (HIV-1) antibody among Minnesota blood donors. Public health and clinical implications

STUDY OBJECTIVE

To evaluate performance characteristics of sequential enzyme immunoassay (EIA) and Western blot human immunodeficiency virus type 1 (HIV-1) antibody testing in a low-risk population.

DESIGN

Three-year prospective study of a selected sample from a community-based population.

SETTING

Two blood collection facilities in Minnesota.

POPULATION

Minnesota blood donors.

RESULTS

During the study period, 630,190 units of blood (donations) from an estimated 290,110 Minnesota-resident donors were screened for HIV-1 antibody. Seventeen Minnesota-resident donors were identified as positive for HIV-1 antibody. Sixteen donors were available for follow-up HIV-1 culture: all were culture positive. The other donor, who was not available for follow-up culture, was likely infected with HIV-1 based on a history of high-risk behavior and positive serologic findings for hepatitis B surface antigen. Using 95% binomial confidence intervals, performance characteristics for sequential EIA and Western blot HIV-1 antibody serology were as follows: false-positive rate by number of donations, 0% to 0.0006%; specificity by number of donations, 99.9994% to 100%; predictive value of a positive test, 81% to 100%.

CONCLUSIONS

In this low-risk population, the false-positive rate of serologic tests for HIV-1 antibody, using HIV-1 culture as the definitive standard for infection status, was extremely low and test specificity was extremely high.

Lack of efficacy of Haemophilus b polysaccharide vaccine in Minnesota

We evaluated the efficacy of Haemophilus b polysaccharide vaccine in children in Minnesota using a case-control study. The vaccine became available in Minnesota in August 1985. During the subsequent 28 months, 88 cases of invasive H influenzae type b disease were identified in children 24 to 71 months of age, the group targeted for vaccination. Of the 88 cases, 36 (41%) occurred in vaccinated children. Fifty-eight (33%) of 176 controls were vaccinated during a similar period. The vaccine's protective efficacy for children with any history of vaccination was -58% (95% confidence interval = -204% to 18%). The vaccine's protective efficacy for children who were most likely to be protected by vaccination was -55% (95% confidence interval = -238% to 29%). Our results indicate that vaccination with Haemophilus b polysaccharide vaccine had no effect in preventing H influenzae type b disease in Minnesota children.

Escherichia coli O157:H7, an emerging gastrointestinal pathogen. Results of a one-year, prospective, population-based study

To examine the incidence of Escherichia coli O157:H7 enteric infections in the United States and to evaluate the vehicles of transmission for sporadic cases, we conducted a one-year, population-based study at a large health maintenance organization (HMO) in the Puget Sound area of Washington State. All stool specimens submitted for culture to the HMO laboratory were screened for E coli O157:H7; the organism was identified in 25 (0.4%) of 6485 stool specimens. All patients with E coli O157:H7 identified had diarrhea; 24 patients (96%) had bloody diarrhea. Exposure histories demonstrated that rare ground beef was consumed more often by patients (21%) than by age-matched control subjects (4%) in the week before onset of illness. Raw milk also was consumed by two patients but by none of the control subjects. Incidence rates for laboratory-confirmed enteric infections in the HMO population were as follows: Campylobacter, 50/100,000 person-years; Salmonella, 21/100,000 person-years; E coli O157:H7, 8/100,000 person-years; and Shigella, 7/100,000 person-years. The organism is a more common pathogen in the United States than is generally recognized, and the diagnosis should be considered for patients with suspected enteric infection.