PUBLIC HEALTH BRIEFS
Antibody to Escherichia coli Enterotoxin in Meat-Packing Workers ROBERT B. WALLACE, MD, MSC, AND SAM T. DONTA, MD
It is nearly 50 years since the suggestion was made that certain strains of E. coli could cause human diarrhea.' It is now apparent that certain E. coli strains are enteropathogenic by three mechanisms: production of heat-stable (ST) or heat-labile (LT) enterotoxins or by direct invasion of the gut, similar to Shigella species.2 The bioassay systems in general have been too timeconsuming, costly, and difficult for application to the large number of specimens potentially generated by epidemiologic studies. A methodologic advance came with the development of in-vitro cell culture techniques for the identification of the heat-labile toxin of E. coli and of antibodies in sera which neutralize it.3 Using this technique, LT antibody determinations in sera are reproducible and correlate well with introduction of enterotoxic E. Coli into human volunteers.3 The in-vitro tissue culture assay has been successfully applied to the study of diarrhea among American Indian children,4 adults with cholera-like diarrhea in India,5 travelers to Mexico,6 and in other epidemic situations. Many health problems associated with employment in meat-packing plants have been described. Among them is the acquisition of brucellosis during slaughtering and processing of cattle and swine.7 E. coli may be part of the "normal" flora of cattle and swine and contamination of raw and cooked meat products by these organisms has been demonstrated.8 In this paper, we examined the sera of employees in a mid-western meat-packing plant for LT antibodies in order to explore the possible risk of exposure to enterotoxigenic E. coli in this population.
Materials and Methods Study Population The sera of 67 men and women employed at a mid-western meat-packing plant, collected between 1965 and 1974 and frozen at -70"C, were available for study. The sera had been collected as part of a routine surveillance program for Brucella infection, a result of prior outbreaks of brucellosis at the plant. Twenty-six persons had at least three specimens collected and preserved over the ten-year period. After available sera were identified, employee records were reviewed for the following variables: age, sex, and specific Address reprint requests to Dr. Robert B. Wallace, Department of Preventive Medicine and Environmental Health, University of Iowa College of Medicine, Iowa City, IA 52242. Dr. Donta is a clinical investigator. Veterans Administration Hospital. This paper, submitted to the Journal May 5, 1977, was revised and accepted for publication July 14, 1977. 68
worksite and duties within the plant. Several employees had multiple tasks within the plant at various times, but if any involved exposure to uncooked animal products, they were so classified for analytical purposes.
Laboratory Methods The adrenal cell tissue culture assay for detecting heatlabile E. coli enterotoxin and antitoxin has been previously described.3' 9 Briefly, the assay is based on the antibody neutralization of a standardized quantity of heat-labile enterotoxin. Absence of antibody allows the enterotoxin to alter the morphology of the adrenal cells. The last dilution of a specimen which neutralizes the enterotoxin effect is designated as the antibody titer of that specimen. All of the serum neutralization tests were performed at the same time in a single laboratory run.
Significance Testing Statistical differences between various analytical groups within the study were determined by application of the standard t-test to the reciprocal geometric mean titers of the individual groups.
Results The age range of the meat-packing employees was 22-57 years. Preliminary analysis was first performed to see if there was any age-specific variation in anti-LT titers independent of exposure to raw animal products. None was found. Figure I shows intraemployment anti-LT titers from the sera of 48 men and 19 women, collected between 1968 and 1972, organized according to whether or not the employees were exposed to raw animal products. Exposure to raw animal products was defined for those persons involved in the slaughtering, butchering, or processing of cattle and hog parts prior to cooking. Those employees not exposed were generally in clerical, security, or delivery activities. Anti-LT titers were significantly higher for both men and women exposed to the raw animal products. While there were insufficient subjects to study titer differences within specific processing operations, the highest anti-LT titers were seen among those with maintenance and janitorial duties. Figure 2 displays anti-LT titer levels in 26 long-term employees on whom three sequential intraemployment serum specimens were available. All but one of these employees were continually exposed to animal products. In the last study period, 1973-74, titers were significantly lower than those of the preceding two periods. More specifically, in the AJPH January, 1978, Vol. 68, No. 1
PUBLIC HEALTH BRIEFS
1:64
*-
1:16
Mo
*0*0
i_
1:4
*00-
000 "00
,-IF-
G
1:64 w
1:16
*--0
.
....
cr*000
1:4
a
*-K-
05@ S...
:-0900
*000 0000
z
@000
-
z
1:1
0000
NEG
0
NEG R.L.G.M.T t
8.30
3.17 *
9.990*
3.33@*
YES NO NO FEMALE MALE EXPOSURE TO UNCOOKED ANIMAL PRODUCTS
YES
FIGURE 1-Intraemployment Serum Anti-Labile-Entertoxin Titers in Meat-Packing Employees
t Reciprocal Log4 Geometric Mean Titer p
Antibody to Escherichia coli Enterotoxin in Meat-Packing Workers ROBERT B. WALLACE, MD, MSC, AND SAM T. DONTA, MD
It is nearly 50 years since the suggestion was made that certain strains of E. coli could cause human diarrhea.' It is now apparent that certain E. coli strains are enteropathogenic by three mechanisms: production of heat-stable (ST) or heat-labile (LT) enterotoxins or by direct invasion of the gut, similar to Shigella species.2 The bioassay systems in general have been too timeconsuming, costly, and difficult for application to the large number of specimens potentially generated by epidemiologic studies. A methodologic advance came with the development of in-vitro cell culture techniques for the identification of the heat-labile toxin of E. coli and of antibodies in sera which neutralize it.3 Using this technique, LT antibody determinations in sera are reproducible and correlate well with introduction of enterotoxic E. Coli into human volunteers.3 The in-vitro tissue culture assay has been successfully applied to the study of diarrhea among American Indian children,4 adults with cholera-like diarrhea in India,5 travelers to Mexico,6 and in other epidemic situations. Many health problems associated with employment in meat-packing plants have been described. Among them is the acquisition of brucellosis during slaughtering and processing of cattle and swine.7 E. coli may be part of the "normal" flora of cattle and swine and contamination of raw and cooked meat products by these organisms has been demonstrated.8 In this paper, we examined the sera of employees in a mid-western meat-packing plant for LT antibodies in order to explore the possible risk of exposure to enterotoxigenic E. coli in this population.
Materials and Methods Study Population The sera of 67 men and women employed at a mid-western meat-packing plant, collected between 1965 and 1974 and frozen at -70"C, were available for study. The sera had been collected as part of a routine surveillance program for Brucella infection, a result of prior outbreaks of brucellosis at the plant. Twenty-six persons had at least three specimens collected and preserved over the ten-year period. After available sera were identified, employee records were reviewed for the following variables: age, sex, and specific Address reprint requests to Dr. Robert B. Wallace, Department of Preventive Medicine and Environmental Health, University of Iowa College of Medicine, Iowa City, IA 52242. Dr. Donta is a clinical investigator. Veterans Administration Hospital. This paper, submitted to the Journal May 5, 1977, was revised and accepted for publication July 14, 1977. 68
worksite and duties within the plant. Several employees had multiple tasks within the plant at various times, but if any involved exposure to uncooked animal products, they were so classified for analytical purposes.
Laboratory Methods The adrenal cell tissue culture assay for detecting heatlabile E. coli enterotoxin and antitoxin has been previously described.3' 9 Briefly, the assay is based on the antibody neutralization of a standardized quantity of heat-labile enterotoxin. Absence of antibody allows the enterotoxin to alter the morphology of the adrenal cells. The last dilution of a specimen which neutralizes the enterotoxin effect is designated as the antibody titer of that specimen. All of the serum neutralization tests were performed at the same time in a single laboratory run.
Significance Testing Statistical differences between various analytical groups within the study were determined by application of the standard t-test to the reciprocal geometric mean titers of the individual groups.
Results The age range of the meat-packing employees was 22-57 years. Preliminary analysis was first performed to see if there was any age-specific variation in anti-LT titers independent of exposure to raw animal products. None was found. Figure I shows intraemployment anti-LT titers from the sera of 48 men and 19 women, collected between 1968 and 1972, organized according to whether or not the employees were exposed to raw animal products. Exposure to raw animal products was defined for those persons involved in the slaughtering, butchering, or processing of cattle and hog parts prior to cooking. Those employees not exposed were generally in clerical, security, or delivery activities. Anti-LT titers were significantly higher for both men and women exposed to the raw animal products. While there were insufficient subjects to study titer differences within specific processing operations, the highest anti-LT titers were seen among those with maintenance and janitorial duties. Figure 2 displays anti-LT titer levels in 26 long-term employees on whom three sequential intraemployment serum specimens were available. All but one of these employees were continually exposed to animal products. In the last study period, 1973-74, titers were significantly lower than those of the preceding two periods. More specifically, in the AJPH January, 1978, Vol. 68, No. 1
PUBLIC HEALTH BRIEFS
1:64
*-
1:16
Mo
*0*0
i_
1:4
*00-
000 "00
,-IF-
G
1:64 w
1:16
*--0
.
....
cr*000
1:4
a
*-K-
05@ S...
:-0900
*000 0000
z
@000
-
z
1:1
0000
NEG
0
NEG R.L.G.M.T t
8.30
3.17 *
9.990*
3.33@*
YES NO NO FEMALE MALE EXPOSURE TO UNCOOKED ANIMAL PRODUCTS
YES
FIGURE 1-Intraemployment Serum Anti-Labile-Entertoxin Titers in Meat-Packing Employees
t Reciprocal Log4 Geometric Mean Titer p
