| Epidemiological Bulletin: Fall 2001 (Part 3 of 4)
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Epidemiology of Tuberculosis in San Mateo County: Foreign Origin, Immigration and Demographic Trends, 1993-2000
Scott Nabity, MPH (Epidemiologist)
This is the second in a series of articles dedicated to the epidemiology of TB in San Mateo County.
Background
In the Summer 2001 edition of the EpiBulletin, we discussed how 94% of local TB cases in 2000 were born outside the U.S., up from 86% in 1999. This proportion is greater than that for California, which has remained around 70%. It also far exceeds that for the U.S., which has increased to slightly less than half of all cases. Consequently, the unique epidemiology of TB in San Mateo County (SMC) greatly influences the nature of local prevention and control efforts, which for maximum effectiveness are increasingly targeted towards a mostly foreign-born case population.
Importation of TB Infection and Disease
During 1993-2000, 255 out of 481 (53%) foreign-born cases occurred in persons born in the Philippines, more than three times the number of cases (n=80; 17%) originating from all 17 other South-East Asian and Pacific Island nations combined (Figure 1). These are followed by Mexico (13%), Central and South America (7.5%), and China (5.8%). India, the second most frequent South-East Asian country of origin for cases born outside the U.S., was origin to only 18 (3.7%) cases during this period. 14 of these occurred during 1997-2000. Locally reported TB disease is concentrated in cities in North County and in South County communities bordering the Bay. It is clear that regionally specific immigration patterns can affect the incidence of imported TB infection and disease. Forty-one percent of all cases resided in Daly City and 11% in South San Francisco; the proportion of foreign-born cases that were Filipino in each city was 75% and 70%, respectively.
Just as with immigration, movement of residents out of a region can similarly impact the burden of TB there. East Palo Alto is the only city in SMC with a majority of U.S.-born cases (60%) over the past 8 years. Approximately half of the 53 cases reported were African-American, while only 25% of EPA residents were identified as being African-American on the 2000 Census. It should be noted that great progress has occurred in this community during the last several years. In 2000, only one TB case was reported in East Palo Alto, steadily down from 12 cases in 1993.
Fig.1: Country of Origin for Foreign-Born Cases,1993-2000. Changing Demographics and Local TB Burden:
Class A/B1/B2 Waiver System:
In order to help prevent importation of infectious active disease among foreign-born persons choosing to reside permanently in the U.S., the Centers for Disease Control and Prevention Division of Quarantine has established a waiver system to ensure that new arrivals who have active TB disease or who are at high risk for TB receive appropriate medical follow-up in the local health jurisdiction of their new residence. Visa applicants >15 years of age must receive a chest radiograph performed overseas (as well as a complete physical and mental assessment, and HIV and syphilis testing).
If the chest radiograph is suggestive of active pulmonary disease, 3 sputa for acid-fast bacillus (AFB) smears (but not cultures) must be obtained. No person with a positive AFB smear is allowed entry, although AFB smear negative active TB cases proven to be responding to an appropriate course of therapy may enter with the permission of the Health Officer of the receiving local jurisdiction. Known as a Class A waiver, very few are allowed entrance to the U.S. through this arrangement. A similar protocol is in place for persons with an abnormal chest radiograph and negative AFB smear results, both administered overseas. Although such individuals have an abnormal chest radiograph suggestive of TB, they are considered non-communicable TB suspects and allowed entry under a Class B1 waiver, and instructed to report to the local health department for medical evaluation within 30 days of arrival. Lastly, Class B2 waivers allow persons with abnormal chest radiographs suggestive of inactive TB to enter under the same arrangements as for Class B1 waivers.
It should be noted that the purpose of this system is to identify persons with active TB in order to interrupt potential transmission, and not necessarily to identify all persons with TB infection. Skin tests administered overseas are generally not considered valid in the U.S. and are not a part of this process. However, A major limitation of the waiver system is that it does not apply to persons entering the U.S. illegally or with temporary visas (including students and high-tech workers who may reside in the US for years, as well as business persons and tourists). For these and other reasons, international borders will remain permeable to TB and other infectious diseases.
Global TB Burden:
The World Health Organization estimates that 8 million people develop TB disease and at least 2 million people (approximately 3 times the population of SMC) die annually. The regions burdened most are sub-Saharan Africa, Central and South-East Asia and portions of South America. The rate of TB in countries of these regions almost invariably exceeds 100 cases per 100,000 people. This figure is 20 times the 2000 U.S. domestic rate of 5.8 cases per 100,000 people, which is an all-time low. Detailed maps depicting country by country incidence of TB can be found at www.who.int/gtb/publications.
Armed with this information, the TB Control Program conducts prevention and control efforts that are culturally and linguistically appropriate for the populations most affected by this disease. In addition, the Division of Public Health has engaged several high-incidence SMC communities and their leaders in joint efforts to address their health priorities. Among these are issues regarding communicable diseases, including TB. The SMC experience clearly illustrates why TB controllers throughout the U.S. agree that the elimination of TB in this country requires enhanced and sustained commitment to effective TB control globally.
Resources and References
U.S. Department of Health and Human Services (2000). Report on TB in the US, 1999.
California Department of Health Services. Report on Tuberculosis in California, 1999 (2000) (p. 19) U.S. Department of Health and Human Services (2000). Core Curriculum on TB, 4th ed.
California Department of Health Services / California TB Controllers Association Joint Guidelines for TB Treatment and Control in California (1998).
Centers for Disease Control and Prevention. Reported TB in the United States, 1999 (2000). (pp.11-13) World Health Organization. Global TB Control, Report 2001 (2000). Geneva, Switzerland. WHO/CDS/TB/ 2001.287.
Leonhardt KK, Gentile F, et al. A Cluster of TB among Crack House Contacts in San Mateo County, California. Am J Public Health. 1994; 84:1834-1836.
Clinical Updates for TB
Scott Nabity, MPH (Epidemiologist)
Liver Injuries Associated With Rifampin (RIF) and Pyrazinamide (PZA) for Latent TB Infection (LTBI): The CDC reported on August 31, 2001 21 cases of liver injury associated with a 2-month RIF-PZA regimen for treating LTBI (1). Of the 21 cases (defined as clinical and laboratory findings consistent with hepatitis leading to hospital admission or death of a patient being treated for LTBI with RIF-PZA) 16 recovered and five died of liver failure. The five patients who died were screened for LTBI and treated with RIF-PZA under guidelines released jointly by the American Thoracic Society and CDC in June 2000 (2). Eleven of the cases reported with liver injury were tested for HIV and all were negative. The cases reported here were nonetheless unexpected, and prompted ATS and CDC officials to revisit the application of this regimen for LTBI. Recommendations that supercede previous guidelines can be accessed in the August 31, 2001 issue of MMWR at www.cdc.gov/mmwr. Possible cases of RIF-PZA induced hepatitis should be reported to the Division of Tuberculosis Elimination at (404) 639-8125.
Testing for TB Recommended for Patients Taking Remicade: The U.S. Food and Drug Administration reported in August 2001 that patients taking Remicade (Infliximab), a treatment for rheumatoid arthritis, are at least four times more likely than average Americans to develop active TB (3). The rate of TB in patients with rheumatoid arthritis is estimated to be approximately that of the general U.S. population. According to the FDA, 70 cases of TB have been reported among people who have taken Remicade and 15 of those have died through May 2001. Unusually, more than 50% of cases were extrapulmonary. Patients for whom Remicade is prescribed should be screened for TB infection and disease with a tuberculin skin test and chest radiograph, and started on therapy for LTBI, if indicated, prior to initiation of Remicade therapy. The FDA's full report can be downloaded at .
References:
1. U.S. Dept. of Health and Human Services. MMWR. Vol. 50 (No. 34); August 31,2001.
2. Targeted Tuberculin Skin Testing and Treatment of Latent Tuberculosis Infection. Am J Resp Crit Care Med . 161:S221-S247; 2000.
3. U.S. Food and Drug Agency, Center for Biologics Evaluation and Research, Arthritis Advisory Committee. Safety Update on TNF - Antagonists: Infliximab and Etanercept; August 17, 2001.
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