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TB Notes 2, 2004

Highlights from State and Local Programs

A Multi-Jurisdictional TB Outbreak Among Seasonal Agricultural Workers From Oaxaca, Mexico

Year round, California employs more than 900,000 migrant and seasonal agricultural workers, 90% of whom are Mexico-born.1,2 In the past two decades there has been a rapid increase in the number of indigenous migrant workers in California: in 2003, approximately 50,000 to 100,000 agricultural workers were of Mixtec descent, originating from the Mexican states of Oaxaca, Puebla, and Guerrero. Mixtecs are Mexicans of indigenous (American Indian) descent. The group consists of many different communities with their own cultures and dialects of the Mixtec language. Catastrophic soil erosion and resultant crop failures in these areas have forced Mixtecs and other indigenous groups to migrate through Baja California and the western United States in order to find work.

Challenges for migrant populations in general are magnified in indigenous groups: they face discrimination from other migrant groups and employers, they receive the lowest wages for the least desirable jobs, and many, particularly the women, speak only their native language and cannot communicate effectively in Spanish or English with employers or health care providers.3

In June 2003, a local health jurisdiction (LHJ) requested assistance from the California TB Control Branch (TBCB) Outbreak Response Team (ORT) to contain an outbreak of TB among Mixtec seasonal agricultural workers. The LHJ had found five persons with TB (3 adults and 2 children) in several related households. The group came from one small village in Oaxaca and traveled frequently among six LHJs in California and one in Washington state. The index case was a young Mixtec male who had a self-reported history of TB treatment in 2002 in Oaxaca. In March 2003, he arrived in California and was subsequently diagnosed with smear- and culture-positive pulmonary TB in May. Despite exhaustive efforts to promote adherence, including detention in a health facility, the index case was lost to follow-up in June 2003. A newly identified secondary case was also lost to follow-up at that time, before being informed of her TB diagnosis. Additionally, a tuberculin skin test (TST)-positive, symptomatic 18-month-old was lost to follow-up before initial evaluation could be completed. The LHJ requested ORT assistance to locate lost cases and suspects, and to identify additional contacts for evaluation. 

Challenges to outbreak containment included frequent client movement between Mexico, California, and Washington; sociocultural, economic, language, and transportation barriers to accessing health care; and difficulty in establishing trust between health departments and clients. Contacts were difficult to elicit, locate, evaluate, and treat, primarily owing to clients’ fear of health authorities because of their undocumented status. To contain the outbreak, the Outbreak Response Team (ORT) facilitated a coordinated approach with the participation of all involved entities, including state TB control programs in California and Washington, affected LHJs, community- based organizations (CBOs), CureTB, and TBNet

To assess the extent of the outbreak, LHJs surrounding the outbreak county and those with known concentrations of migrant workers were canvassed for Oaxaca-born TB cases diagnosed in 2003. A TB outbreak alert was distributed to all Health Officers in California and community health care providers within affected LHJs, requesting rapid reporting of anyone from Oaxaca newly diagnosed with TB. Isolates from persons from Oaxaca with culture-confirmed TB with known or suspected epi-links were genotyped by CDC. The TBCB ORT, State of Washington TB Control, and LHJs held regular meetings and teleconferences to set outbreak investigation priorities and exchange information. A centralized outbreak database was maintained by the TBCB ORT and used to track patient movement and evaluation status. 

In cooperation with the Fresno Health Department Communicable Disease Outreach Program, the Binational Center for Indigenous Oaxacan Development (CBDIO) in Fresno, California, provided TB education and outreach to Mixtec audiences. This was accomplished through radio and TV broadcasts in Spanish and Mixtec and  a TB patient education audiotape that was recorded and distributed to health departments. Mixtec interpreters were located through CBOs, including the CBDIO and California Rural Legal Assistance. Oaxacan community leaders were enlisted and the TBCB provided additional funds to the primary outbreak LHJ to hire a Oaxacan consultant to enhance LHJ cultural and language competence. LHJs and the TBCB ORT worked with TBNet to improve continuity of care as patients moved between US locations by enrolling them in the TBNet program.

It was also necessary to coordinate TB care in Oaxaca for persons with TB disease returning home before completion of treatment. Access to health care in the home village is limited, with the nearest clinic four hours away by bus. CureTB coordinated closely with health care staff in the home village area, who in turn coordinated with village leaders to ensure continuing therapy for persons with TB disease.

As of December 2003, 68 individuals were identified through this outbreak investigation and 56 completed evaluation. Ten (18%) have TB disease (5 culture-confirmed adults with pansusceptible disease, 5 clinically diagnosed pediatric cases), two (4%) are TB suspects, and 34 (61%) have latent TB infection. Eight of 10 outbreak cases and one TB suspect moved one or more times during evaluation and treatment. The index case was found in his home village in Mexico and was restarted on treatment; however, after only about 2 months of therapy it was reported that he had left his village and was returning to California. Efforts are currently underway to locate him. Thanks to information obtained through our active surveillance efforts, the lost secondary case was located in Washington state and started on therapy in August 2003. She returned to California in September and subsequently went back to Mexico in October, where her treatment continued as a result of close coordination between CureTB and health care providers in Mexico. In January 2004, she returned to California where therapy continues. The 18-month-old was located and evaluated in August 2003 and remains on treatment for clinically diagnosed TB.  All other cases remain on treatment.

Genotyping results on isolates from the five culture-confirmed adult outbreak cases show an identical DNA fingerprint among four of the isolates, suggesting transmission between these individuals or from a common source, or a TB strain endemic to the home village. Additionally, an isolate from a 2001 pleural case diagnosed in Washington state who came from the same village has a matching RFLP pattern with this outbreak strain.

This outbreak revealed a very high proportion of tuberculin skin test-positive individuals (80% of those evaluated). Interruptions in treatment, delays in diagnosis, and crowded living conditions contributed to extensive transmission in this outbreak. Breaks and delays in treatment were related to fear of authorities, lack of financial resources, lack of transportation, long work hours, language barriers, lack of TB knowledge, and frequent movement. Results from this investigation highlight the difficulties in containing TB outbreaks in migrant workers and indicate the importance of collaboration between community partners and health jurisdictions at local, state, and national levels for containment of an outbreak among a highly mobile population. Involving community leaders, providing adequate interpretation, and using all available media to communicate key messages are effective methods for creating awareness and establishing trust within a hard-to-reach population, and thus decreasing lost cases and suspects and halting transmission. 

The genotyping results and anecdotal information obtained from case interviews suggest that in addition to U.S.-based transmission, there may be ongoing TB transmission in the home village. Continued coordination with health authorities in Mexico will be critical to ensuring containment of the outbreak on both sides of the border.

—Submitted by Tina Albrecht, MSPH, Public Health Advisor
and D’Arcy Richardson, RN, PHN, MS, CNS,
TB Outbreak Response Officer/Nurse Epidemiologist
California State TB Control Branch


1. Migrant and Seasonal Farmworker Enumeration Profiles Study – California. September 2000.

2. California Institute for Rural Studies, Rural California Report. Who Does California Farmwork. Fall 2001; vol 12 (3).

3. Zabin C, Kearney M, Garcia A, Runsten D, and Nagengast C. Mixtec migrants in California agriculture: a new cycle of poverty. Davis, CA: California Institute for Rural Studies; 1993.


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