v21n15

DEPARTMENT OF PATHOLOGY
The Johns Hopkins Medical Institutions

Vol. 21, No. 15
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, May 7, 2002

Provided by Karen Fujii, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

6 outbreaks were reported to DHMH during MMWR Week 18 (April 28 - May 4):

2 GASTROENTERITIS outbreaks:

1 at a hospital in Anne Arundel Co. (1 lab-confirmed case of Clostridium difficile),

1 at a nursing home in Carroll Co.

1 SHIGELLOSIS outbreak (2 lab-confirmed cases of Shigella sonnei) at a daycare in Baltimore City

1 FOODBORNE GASTROENTERITIS outbreak associated with a fast-food restaurant in Anne Arundel Co.

1 PERTUSSIS outbreak (1 lab-confirmed case) in a private home in Prince George's Co.

1 PNEUMONIA outbreak (7 chest X-ray confirmed cases; 1 Influenza A + case) at a nursing home in Carroll Co.

The Johns Hopkins Hospital, Department of Pathology, Information provided by, Lynette S. Nichols, MD.

Case description: The patient is a 61-year-old man without a significant past medical, family or social history. Previous animal exposure or contact is unknown and prior vaccination with BCG was not documented, however was unknown. The patient was diagnosed with colorectal cancer in early 2002. A hemicolectomy was performed and metastatic disease was identified in multiple mesenteric lymph nodes. Subsequent liver metastasis were noted, and a segmental liver resection was performed. The post surgical course was complicated by portal vein thrombosis and colonic perforation at the site of previous resection. The patient's condition continued to decline ultimately requiring mechanical ventilation. A decision was made to withdraw support and the patient subsequently died. A postmortem examination was performed revealing widely metastatic carcinoma and ischemic bowel. An incidental finding noted was a 3cm caseating granuloma in the cecum. There were no similar lesions in the lungs or lymph nodes. However, the lesion was predominantly calcified, and failed to reveal organisms. In light of the solitary nature of the caseating granuloma, the lack of granulomata elsewhere and history of immunocompetance, the presumed organism is Mycobacterium. Specifically, a likely species producing gastrointestinal disease is Mycobacterium bovis although exposure history to animals or BCG vaccination is not known for this patient. These findings could not be confirmed by postmortem examination and were not thought to contribute to the cause of death.

Organism: Mycobacterium bovis is known as the agent of bovine tuberculosis. M. bovis was a significant cause of "tuberculosis" worldwide in the early 1900s and before. Destruction of animals infected with M. bovis and subsequent pasteurization procedures for milk decreased the human infection rate by M. bovis dramatically. M. bovis was thought to be transmitted not only by ingestion of infected milk but also aerogenously by cow to human transmission. Human to human transmission is quite controversial. The potential for human to cow transmission also may occur through aerosols, as well as through urine of farmers with genitourinary M. bovis disease, where feeding areas are contaminated by infectious urine, which is either aerosolized or ingested by cattle. Other animal reservoirs may include pigs, goats, deer, cats, dogs, foxes, badgers, marsupials, rabbits, sheep, and horses.

Clinical manifestations: Unlike tuberculosis, much of the primary disease caused by M. bovis occur in the cervical lymph nodes and the GI tract with its related lymphatics; however, M. bovis may cause pulmonary disease and cause disease in other extrapulmonary sites in a similar manner to MTB. The most common sites of M. bovis infection in children are involvement of the cervical lymph nodes and intra-abdominal organs as reflected in the oral portal of entry. Incidence is extremely low since eradication of infected cattle and widespread pasteurization of milk. Disease can occur, however, in any organ system similar to MTB. In adults, extrapulmonary M. bovis infection is often through reactivation. The lung is still the most common organ involved when transmission is through bovine contact. M. bovis can cause gastric TB, tuberculous meningitis, miliary disease, epidural abscess and spinal tuberculosis, bone and joint infections, and genitourinary infection.

Mycobacterium bovis Diagnosis: Mycobacterium bovis is an acid-fast bacillus, often shorter and plumper than M. tuberculosis (MTB). M. bovis grows more slowly than most mycobacterial species and growth can be inhibited by the presence of glycerol in the media. It is biochemically differentiated from MTB by niacin and nitrate reduction tests (M. bovis is usually negative for both tests where MTB is generally positive). Unlike MTB, M. bovis is microaerophilic, sensitive to thiopin-2-carboxylic acid, and resistant to pyrazinamide. M. bovis grows only at 35°C and appears as tiny translucent, smooth, pyramidal colonies. These organisms grow well on most media commonly used for the culture of MTB, including the Lowenstein-Jensen and 7H11. BCG is an attenuated mutant of M. bovis.

The diagnosis should be based on appropriate history of animal exposure, occupational contact, or receipt of BCG vaccination or chemotherapy. The tuberculin skin test may be useful, except in patients with known exposure to BCG. Appropriate specimen retrieval from suspected infected sites is necessary, with subsequent acid-fast staining and cultures. M. bovis will grow in a routine mycobacterial culture.

References:

Koneman et al. Color Atlas and Textbook of Diagnostic Microbiology, 5^th Edition, Lippincott-Raven, Philadelphia, 1997.

Brown BA and Wallace RJ. In, Principles and Practice of Infectious Diseases, 5^th Edition. Edited by GL Mandell, JE Bennett, and R Dolan. Churchill Livingstone, inc., Philadelphia, 2000.

M. H. Hinton. Infections and Intoxications Associated with Animal Feed and Forage which may Present a Hazard to Human Health. The Veterinary Journal 2000, 159, 124-138.