Brucellosis Outbreak at a Pork Processing Plant -- North Carolina, 1992

During 1992, the North Carolina Department of Environment, Health, and Natural Resources (NCDEHNR) received reports from the Sampson County Health Department of 18 cases of brucellosis among employees at a local pork processing plant; onsets of illness occurred from November 1991 through September 1992. Clinical features and serologic testing of all patients were consistent with brucellosis, and Brucella suis was isolated from blood samples obtained from 11 persons at the time of acute illness. Two patients were hospitalized. All of the affected employees had documented exposure to the kill floor of the plant. In March 1993, plant employees requested that CDC's National Institute for Occupational Safety and Health (NIOSH) evaluate occupational transmission of brucellosis at the facility.

The NIOSH investigation was conducted during May-June 1993 and included a questionnaire survey, serologic testing, and an industrial hygiene survey. Serologic status was determined using the standard tube agglutination (STA) test *. The 2-mercaptoethanol (2-ME) test was also used to assist in differentiating recent or persistent infection from past infection with low-titered antibody. ** A case of brucellosis was defined as an STA titer greater than or equal to 160:1 and either 1) two or more symptoms (fever, chills, headache, myalgia/arthralgia, fatigue, anorexia, sweats, weight loss, and weakness) during the preceding 12 months or 2) a positive 2-ME test (2-ME titer greater than or equal to 20:1). ***

Of the 156 workers in the kill division, 154 (99%) participated in the survey; of these, 30 (19%) met the case definition for brucellosis, including 16 (53%) with previously unrecognized cases. Twelve of these 16 had been symptomatic. Within the kill division, risk for brucellosis was highest among workers in the head (33%) and red offal (25%) departments (Table_1). Twenty-nine of the 30 employees with cases reported a history of ever having been cut or scratched at work, compared with 102 of 124 employees without cases (odds ratio=6.3; 95% confidence interval=0.9-267) (Table_1).

NIOSH investigators distributed educational material concerning swine brucellosis to all kill floor employees, notified participants of their individual results by mail, and met with individual employees to supplement the mail notifications. Information about swine brucellosis was provided to local physicians. NIOSH staff recommended that the plant process only brucellosis-free swine. In addition, NIOSH staff provided recommendations to management and employees concerning personal protective equipment usage (i.e., rubber gloves and face shields), the need to maintain the kill floor at negative pressure with respect to the contiguous building, and the importance of ongoing education.

The plant processes approximately 8000 swine per day, and the animals originate in at least 10 states. NIOSH and NCDEHNR are working with the U.S. Department of Agriculture (USDA) to determine the possible source of infected swine processed at the plant.

Reported by: L Hunter, DVM, CG Smith, MD, JN MacCormack, MD, State Epidemiologist, North Carolina Dept of Environment, Health, and Natural Resources. Animal and Plant Health Inspection Svc, US Dept of Agriculture. National Center for Infectious Diseases; Hazard Evaluations and Technical Assistance Br, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: Brucellosis (also termed undulant, Mediterranean, or Malta fever) is a febrile illness caused by several species of bacteria of the genus Brucella ****. The incubation period is typically more than 30 days but can range from 5 days to several months. Symptoms are nonspecific and include fever, chills, sweats, headache, myalgia/arthralgia, anorexia, fatigue, and weight loss. The most common physical findings (other than fever) are lymphadenopathy and splenomegaly. Subclinical Brucella infection occurs commonly, and the ratio of subclinical to clinical infection varies from 1:1 to 12:1 (1). The antibiotic regimen recommended by the World Health Organization is a 6-week course of doxycycline (100 mg every 12 hours orally) and rifampin (15 mg/kg of body weight per day {maximum: 600 mg} in a single morning dose) (2 ). Even with treatment and clinical improvement, fatigability may persist for a month or more and be accompanied by pronounced disability; relapsing illness occurs in approximately 2%-10% of patients treated with recommended antibiotic regimens (3).

Definitive diagnosis requires isolation of the causative organism in cultures of blood or bone marrow. However, brucellosis is more commonly diagnosed serologically, either by a fourfold rise in STA titer over several weeks or a single titer greater than or equal to 160:1 in a person with compatible clinical manifestations (4).

In the United States, human brucellosis is a reportable disease in every state except Nevada. In 1992, 105 cases were reported to CDC by state health departments (5), compared with a peak of approximately 6300 in 1947 (6). However, because of the variable clinical manifestations of brucellosis, only an estimated 4%-10% of cases are recognized and reported in the United States (7). The findings in this report indicate that occupational transmission of brucellosis remains a public health hazard, particularly among persons exposed to swine.

Person-to-person transmission of brucellosis is rare (8), and a substantial proportion of reported cases are associated with ingestion of unpasteurized dairy products contaminated with B. melitensis that have been imported from Mediterranean countries or Mexico (6). Occupational transmission of brucellosis occurs primarily among packing plant workers, veterinarians, livestock producers, and laboratory workers. Among packing plant workers, transmission of brucellosis occurs from infected swine to workers through breaks in the workers' skin, inhalation, and conjunctival contact (9). The primary strategy for prevention of brucellosis in workers is to reduce exposure to infected animals by eliminating commercial slaughter of such animals. Although personal protective equipment is often recommended, the efficacy of personal protective equipment in preventing the occupational transmission of Brucella requires further assessment.

A unified national program to eradicate swine brucellosis was initiated in 1961. The Cooperative USDA Animal and Plant Health Inspection Service-State Animal Health Swine Brucellosis Eradication Program, in which all states participate, has established surveillance and procedures necessary for locating infected herds, controlling infected and exposed swine, and eliminating infected swine (10). In addition, specific provisions exist to designate entire states or individual swine herds as brucellosis-free. As of December 31, 1993, 34 swine herds nationwide were under quarantine for brucellosis in seven states (Florida, Georgia, Hawaii, Oklahoma, South Carolina, Tennessee, and Texas). These brucellosis-infected herds can be moved for slaughter only under permit issued by USDA. In general, processing plants that receive brucellosis-infected herds do not employ special precautions to prevent occupational exposure to the infected swine, potentially placing workers at increased risk for infection. USDA is evaluating its swine brucellosis control/eradication program, including the disposition of known brucellosis-infected herds.

References

1. Buchanan TM, Faber LC, Feldman RA. Brucellosis in the United States, 1960-1972: an abattoir-associated disease. Part I. Clinical features and therapy. Medicine 1974;53:403-13.

2. Ariza J, Gudiol F, Pallares R, et al. Treatment of human brucellosis with doxycycline plus rifampin or doxycycline plus streptomycin. Ann Intern Med 1992;117:25-30.

3. Moyer NP, Holcomb LA. Brucellosis. In: Balows A, Hausler WJ, eds. Diagnosis of infectious diseases -- principles and practice. Vol

4. New York: Springer Verlag, 1988:143-54.

5. Young EJ. Serologic diagnosis of human brucellosis: analysis of 214 cases by agglutination tests and review of the literature. Rev Infect Dis 1991;13:359-72.

6. CDC. Summary of notifiable diseases, United States, 1992. MMWR 1992;41(no. 55):67.

7. Kaufmann AF, Wenger JD. Brucellosis. In: Last JM, Wallace RB, eds. Public health and preventive medicine. Norwalk, Connecticut: Appleton and Lange, 1992:263-4.

8. Wise RI. Brucellosis in the United States -- past, present, and future. JAMA 1980;244:2318-22.

9. Ruben B, Band JD, Wong P, Colville J. Person-to-person transmission of Brucella melitensis. Lancet 1991;337:14-5.

10. Kaufmann AF, Fox MD, Boyce JM, et al. Airborne spread of brucellosis. Ann N Y Acad Sci 1980;353:105-14.

11. Swine Brucellosis Control/Eradication. State-federal-industry uniform methods and rules. Washington, DC: US Department of Agriculture, Animal and Plant Health Inspection Service, August 1993; publication no. (APHIS)91-55-016 (revised).

* This test uses a B. abortus antigen to detect infections with B. abortus, B. melitensis, and B. suis. 

** The use of 2-ME in the STA disrupts the disulfide bonds of immunoglobulin M and allows measurement of only immunoglobulin G (IgG), which appears within weeks after infection. In patients who have been adequately treated and achieved a clinical cure, IgG generally declines, although it can persist for up to 1 year; in the absence of adequate treatment, IgG usually persists. IgG, as detected by the 2-ME test, is therefore used as a marker for persistent or recent infection. 

*** The case definition used in this investigation differs from the national surveillance case definition, which is based on a compatible clinical illness supported by culture or serologic evidence. 

**** Brucella species known to cause human disease (and their usual reservoir hosts) are: B. abortus (cattle), B. canis (dogs), B. melitensis (goats and sheep), and B. suis (swine). The distribution of disease caused by the various Brucella species varies from region to region.
Table_1
Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 1. Number of employees in the kill division who reported ever being cut
at work, by department and by persons with and without brucellosis --- North
Carolina pork processing plant, 1993
==========================================================================================
                                         Cases*              Noncases
                                -------------------  -------------------
                        No.               No.                  No.
Department           employees  No.  reporting cuts  No.  reporting cuts
------------------------------------------------------------------------
Kill--Mezzanine          37      7         7          30        26
White offal              32      6         6          26        23
Head                     21      7         6          14        11
Red offal                16      4         4          12        10
Kill--Machine            12      1         1          11        10
Kill--Other              11      2         2           9         6
Maintenance               8      1         1           7         6
Kill--Scale               7      1         1           6         3
Kill--Bleed               4      0         0           4         2
Pet food                  3      1         1           2         2
Supervisors               3      0         0           3         3

Total                   154     30        29         124       102
------------------------------------------------------------------------
* Standard tube agglutination test >=160:1 and either 1) two or more symptoms consistent
  with brucellosis or 2) a positive 2-mercaptoethanol test.
==========================================================================================

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