In this issue...
Warning Issued Against Some Imported Cheese
Window-period Prophylaxis following Exposure to Active Tuberculosis
Targeted Testing: Deciding Who’s from a High Prevalence Country
In recent months, several states ( New York and Maryland) have reported TB cases, including deaths, caused by Mycobacterium bovis. These cases have possibly been associated with the consumption of imported soft cheese. The imported soft cheeses, including queso fresco, queso blanco, cotija, and crema Mexicana, are commonly manufactured with unpasteurized milk. The cheese frequently originates in Central American counties, including Mexico, Nicaragua and Honduras and is often sold in the United States at flea markets, door-to-door and from the back of trucks without approval of the normal food inspection programs.
Humans may acquire M. bovis by eating or drinking unpasteurized (raw) milk products produced in countries or regions where M. bovis disease is common in cattle. Young children and immunosuppressed individuals are at higher risk for the disease.
M. bovis infection can cause respiratory and/or gastrointestinal illnesses. Symptoms include:
M. bovis tuberculosis is diagnosed by isolating bacteria from sites of infection in a patient in the same way as M. tuberculosis disease and is usually treated with standard first-line anti-tuberculosis medications.
Patients should be counseled that some dairy products made with raw (unpasteurized) milk are often contaminated with bacteria. These raw (unpasteurized) dairy products represent a serious health risk, especially to high-risk groups such as children, pregnant women, older adults, and immunosuppressed persons. In addition to M. bovis, other infections can be transmitted through unpasteurized dairy products. These include brucella, listeria, E. coli, salmonella, and staphylococcus.
For information on the MarylandM. bovis cases:
http://edcp.org/tb/bovine_tb.html
For information on the New YorkM. bovis cases:
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5424a4.htm
For FDA food safety information related to soft cheese:
http://www.fda.gov/bbs/topics/news/2005/NEW01165.html
The timely identification, evaluation and treatment of contacts are cornerstone activities used by health departments to disrupt the transmission of tuberculosis within communities. For selected contacts at high risk for development of active disease following an exposure, the use of window prophylaxis is another important strategy in efforts to reduce transmission and morbidity within communities.
The new CDC Contact Investigation guidelines recommend window-period prophylaxis as an option for contacts with a negative TST result < 8 weeks after the end of exposure. Treatment should be started as soon as the individual is fully evaluated to rule out active disease. Before any treatment for TB infection or window prophylaxis is initiated, the contact should be fully evaluated to rule out active disease. This evaluation should include a symptom screening, physical examination, TST, chest x-ray and other diagnostic tests such as sputum as needed. Window prophylaxis should only be considered if the TST is negative and there is no evidence of active TB disease on the symptom screen, physical exam and chest x-ray. Window prophylaxis can be stopped if a second TST, performed 8-10 weeks after the end of exposure, is negative.
Window-period prophylaxis is recommended for contacts < age 5. A full course of treatment for presumptive M. tuberculosis infection is recommended for HIV-infected or otherwise immune-suppressed contacts even if TST results are negative >8 weeks after the end of exposure.
For additional information, consult the newly published CDC Contact Investigation guidelines.
Recommendations for the Investigation of Contacts of Persons with Infectious Tuberculosis, MMWR 2005; 54 (RR-15) http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5415a1.htm
As part the risk assessment and target screening process, questions often arise concerning the definition “high prevalence country” for the purposes of completing the risk assessment tool and determining who should receive a tuberculin skin test (TST).
An easy rule of thumb is to consider all countries high prevalence except the US, Canada, Western Europe, Australia and New Zealand.
The following is a more complete listing of exception countries based on data from the 2004 World Health Organization (WHO) Global TB Control Report. A country was considered “low prevalence” if its case rate was less than three times the US case rate. Individuals from these countries should only be tested if they are symptomatic or have another individual risk factor. As updated data from the WHO becomes available, countries may need to be added and deleted from this list. For updated case numbers and case rates, consult the WHO web site at http://www.who.int/tb/en/
(i)Based on 2004 WHO Global TB Control Report. Countries included in exception list have a case rate less than 3 times the U.S. rate.