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Brucellosis in an urban setting

Prince Salman Hospital, which serves southwest Riyadh city, noted increasing numbers of brucellosis cases during 1993 and requested a study to determine the risk factors for brucellosis in this urban setting.
We identified all positive (>=1:160) Brucella agglutination tests from the hospital laboratory logbook for 1993 and from those chose 52 patients (case-persons) with a clinical history of brucellosis.
We interviewed all case-persons about their exposure to dairy products, meat and livestock during the 60 days before the first symptom. We also asked about their habitual exposure to these same things.
We selected as household control-persons two persons of the same sex and approximate age from the same household as each case. We also selected 52 community control-persons from among visitors to two primary health clinics in the same districts from which most of the cases came. We interviewed all control persons using the same questions covering the same possible exposure period for the corresponding case.
The incidence rate of laboratory-diagnosed brucellosis from the Prince Salman Hospital catchment area was 78.51100,000 population in 1993. Males accounted for 65% of brucellosis cases.
Sixty-nine percent of case-households kept livestock, compared with 19% of community control households (odds ratio [OR] = 9.5, 95% confidence interval [CI] 3.2-24). Sick livestock were reported by 32 of 36 case households, compared with none of the 10 community control households that reported raising livestock (p<0.001).
We next looked at 36 households that raise livestock for risk factors specific to contact with livestock. In these households 83% of case-persons performed general livestock care, compared with 9% of household control-persons (OR = 51, 95% Cl 13-217).
Because the livestock were kept outside the city, usually only one family member was responsible for animal care. Among specific livestock care activities, cleaning livestock pens (OR=27, 95% CI 32-1,263) and slaughtering livestock (OR=inf) had the highest odds ratios. Other activities were attending birth of livestock (OR=40.3, 95% CI 10-177) and milking livestock (OR=82.5, 95% CI 10-1,804).
Given the strong association with livestock, we stratified additional analyses of exposure to raw meat and raw milk by livestock ownership. The OR for eating raw liver among households that raised livestock was 4.9 (95% CI 1.6-3.8).
We found no other association of brucellosis with eating raw meat, raw milk or dairy products. However, persons who had a sore or bleeding gums or other lesions in the mouth and drank raw milk in households that kept livestock had an increased risk of brucellosis (OR = 19, 95% Cl 2.3-849). The association was not seen in houses without livestock or with community controls.

Editorial note:

Brucellosis is endemic in the Middle East.[1,2) In Saudi Arabia, the prevalence (percent) of brucellosis, based on a nationwide survey in 1992, was found to be 2.5% in the central region, 2.3% in the southern and eastern regions, 1.6% in the northern region and 0.6% in the western region.[3]
In Saudi Arabia 92% of cases are due to infection with B. melitensis and 8% are due to B. abortus; B. suis of hogs has not been isolated.[1]
This study found that the incidence of laboratory-diagnosed brucellosis in southwestern Riyadh City (central region) was about 0.8% in 1993. However, patients with brucellosis usually undergo more than one serologic test either to confirm the diagnosis or for follow-up purposes. Moreover, serologic tests can be positive long after recovery.
Without exclusion of repeated tests, incidence rates of brucellosis may have been overestimated. The surveillance system at Riyadh Al Kharj Hospital developed a computer program to identify only newly diagnosed cases of brucellosis based on serologic tests. As a result, a dramatic fall (by about 75%) in the number of reported cases was observed [4].
Risk factors for brucellosis in Saudi Arabia included: intake of unpasteurized (raw) milk or milk products, contact with livestock (including breeding, milking, attending birth, touching placental membranes of animals) or cutting raw meat[2,3]. However, according to this study, drinking raw milk is not a risk factor for brucellosis. This result should be taken with caution as it presents a disagreement with other studies cited repeatedly in medical literature.
The low prevalence of brucellosis in urbanized western Saudi Arabia was attributed to the less common practice of drinking raw milk.[1] However, raw milk may not serve as a good medium for brucella after it turns sour (laban).
Interventions to control the disease should include socially acceptable health educational programs to increase awareness among people about the modes of disease transmission.
  1. Oldfield EC, Wallace MR, Hyams KC, Yousif A, Lewis DE, Bourgeois AL. Endemic infectious diseases of the Middle East. Rev Infect Dis 1991; 13 (suppl 3), S197-S217.
  2. Al-Sekait MA. Epidemiology of brucellosis in northern Saudi Arabia. Saudi Med J 1992; 13:296-9.
  3. Al-Aska A, Al-Sekait M, Almuflih I, Al-Balaa 5, Al-Nasser A. Epidemiology of brucellosis in Saudi Arabia, the scientific report (in Arabic). Ministry of Health and King Saud University, Saudi Arabia. 116 pages (1992).
  4. Asogwa SE. Communicable diseases notification in RKH the zoonosis. Riyadh Al Kharj Hospital Programme Epidemiological Bulletin 1993; 2(3)17-19.