Kristine L. MacDonald

A National Outbreak of Salmonella enteritidis Infections from Ice Cream

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 (Schwans) 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 Schwans 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.

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 companys 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.

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.

Sporadic Cases of Hemorrhagic Colitis Associated with Escherichia coli 0157:H7

After two outbreaks of hemorrhagic colitis associated with a previously unrecognized pathogen, Escherichia coli O157:H7, a surveillance system was established to identify and study sporadic cases of this distinct clinical illness in the United States. Between August 1982 and April 1984, we identified 28 persons from 11 states who met our case definition and whose stool specimens yielded E. coli O157:H7. Patients ranged in age from 1 to 80 years. Seventeen patients required hospitalization. All patients recovered, although one developed hemolytic-uremic syndrome 7 days after the onset of bloody diarrhea. Detection of E. coli O157:H7 in stools from persons with hemorrhagic colitis was highly associated with collection of stool specimens within the first 6 days after onset of illness. All E. coli O157:H7 isolates produced a Vero cytotoxin. Hemorrhagic colitis caused by E. coli O157:H7 is widely distributed in the United States as a sporadic illness; clinicians should be aware of its distinctive clinical presentation, and should collect specimens promptly when the diagnosis is suspected.

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.

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.

Botulism and botulism-like illness in chronic drug abusers.

From 1982 to 1983 we received reports of a neurologic illness characterized by a symmetric descending paralysis in six drug abusers from widely separated geographic areas. Botulism was confirmed in two patients; type B botulinal toxin was found and Clostridium botulinum was isolated from a small abscess in one, and type A botulinal toxin was found in the serum of the other. The clinical illness in the remaining four patients, although not laboratory confirmed, was also compatible with botulism. None of the patients had histories suggestive of foodborne botulism, and wound botulism was suspected as the cause of illness. There are several reports of tetanus associated with parenteral drug abuse; wound botulism is another toxin-mediated clostridial infection that may occur as a complication of chronic drug abuse.

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 (Schwans) 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 Schwans 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.

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.

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.