In-Country Migration and Risk Factors for HIV Acquisition among Pregnant Women in Tijuana,Mexico

Introduction

AIDS is a major health concern along the US-Mexico border. Mexico ranks third in the Americas with regard to the number of AIDS cases, with 157 529 cases accumulated as of June 2012. ¹ According to the Mexican National Center for AIDS Prevention (CENSIDA), Baja California including Tijuana has the second highest rate of AIDS in Mexico, with 205 cases per 100 000. This is 46% higher than the Mexican national average and second only to the Federal District. ¹

As of December 2010, the US census indicated that more than 11 million Hispanics of Mexican descent resided in California, which represents a 54% increase over the last decade, mostly due to migration. With economic and social factors being the driving force for migration, ² Baja California is a leading point of entry into the United States, with the Tijuana–San Diego border crossing being the busiest land port of entry in the world, with over 42 million north-bound legal border crossings during 2011. ³ Tijuana has a highly mobile population, with 45% of its population being born in another Mexican state or country. ⁴ Previous research has documented that drug use and commercial sex are more prevalent in the border region compared to other Mexican communities. ⁵ Therefore, Tijuana offers a unique opportunity to study the HIV acquisition risk behaviors and migration patterns at the US-Mexico border.

Migration has been linked with HIV acquisition risk behaviors in sub-Saharan Africa, Asia, and Latin America. ^{6 –8} HIV acquisition risk behaviors had been studied among mostly male Mexican migrants in the context of international migration to the United States, either while in the United States or upon their return to Mexico. ^{8 –10} The implications of internal Mexican migration to the US-Mexico border region on HIV acquisition risk factors among women of childbearing age have received little attention. ¹¹ The aim of our study was to compare the HIV prevalence and HIV acquisition risk behaviors between pregnant women residents and migrants in Tijuana, Mexico.

Methods

A cross-sectional study of pregnant women seeking prenatal care or admitted to the labor and delivery unit was conducted at Tijuana General Hospital, Baja California, Mexico, between September 2007 and July 2008. Tijuana General Hospital is a public hospital that serves uninsured persons who lack social security and are economically disadvantaged. The obstetric department has an average of 500 deliveries per month, of which only 60% has some degree of prenatal care. ¹² Pregnant women with unknown HIV status seeking prenatal care or who were admitted to the labor and delivery unit with an estimated gestational age >28 weeks were invited to participate, and HIV counseling was given by a research nurse and by the senior obstetrics and gynecology resident. Based on research personnel availability, sampling was limited from Monday 8 am to Friday 4 pm. Informed consent was obtained from all participants, and the study protocol was approved by the University of California San Diego Human Research Protection Program and the Tijuana General Hospital Committee of Medical Education and Research.

After a signed informed consent was obtained, blood was drawn by venipuncture; plasma was separated and screened for HIV antibodies by the rapid test Uni-Gold Recombigen HIV (Trinity Biotech Plc, Ireland) according to the manufacturer’s instructions. A rapid positive test result was followed by a confirmatory enzyme immunoassay (Abbott Diagnostics, North Chicago, Illinois) and Western blot (Focus Technologies, Cipres, California), according to the Mexican national guidelines and World Health Organization criteria. ^13,14

Demographic data, lifetime HIV acquisition risk behaviors, clinical data, and delivery information were prospectively collected using a standardized form administered by the research nurse and obstetrics and gynecology resident. Migrants were defined as women who had resided in Tijuana for less than 5 years, while Tijuana residents were defined as those living in Tijuana for more than 5 years.

Results

From September 2007 to July 2008, a total of 3331 pregnant women consented to participate, representing 95% of the women approached. There were 2502 (75%) Tijuana residents and 829 (25%) migrants from different Mexican states. The majority of migrants originated from Chiapas (14.6%), Sinaloa (13%), Jalisco (9.5%), Veracruz (7.4%), Michoacan (7.2%), Nayarit (5.5%), Guerrero (4.8%), and Baja California, other than Tijuana (4.6; Figure 1). In addition, 5.9% of migrants resided in the United States prior to arriving in Tijuana. Among the 2483 Tijuana residents with reported birth places, 1543 (62.1%) were born elsewhere, including Sinaloa (17.2%), Jalisco (10.2%), Michoacan (8.2%), Nayarit (7.7%), Chiapas (7%), Veracruz (6.2%), and Mexico Distrito Federal (5.8%). Therefore, 2372 (71.2%) women delivering at Tijuana General Hospital were either migrants or were born outside of Tijuana. Migrants were significantly younger (22.7 versus 23.4 years, P = .005) and reported more lifetime sexually transmitted infections (4.45% versus 2.51%, P = .006) compared to Tijuana residents. Tijuana residents had younger age at sexual debut (16.7 versus 17.2 years, P < .001), higher parity (2.30 versus 2.08, P < .001), higher methamphetamine use (5.63 versus 2.97%, P = .003), and a spouse who used methamphetamine (10.4 versus 6.5%, P = .002; Table 1). No differences were observed in the proportion of migrants enrolled during labor or at the prenatal clinic, in the number of prenatal visits, or in the number of sex partners in the previous 2 years. When asked whether these women were planning to immigrate to the United States, 145 (6.2%) Tijuana residents and 54 (6.9%) migrants responded affirmatively (P = .44). The HIV seroprevalence did not differ between Tijuana residents (18 of 2502, 0.72%) and migrants (3of 829, 0.36%, P = .32). Maternal HIV acquisition risk behaviors included methamphetamine use (adjusted odds ratio [OR]: 6.03, 95%: 2.3–15.8, P < .001) and first presentation at labor (adjusted OR: 5.0, 95%: 1.6–15.3, P = .005) in multivariate regression analyses that adjusted for migrant status, age, age at sexual debut, parity, and reported history of sexually transmitted infections.

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Figure 1.

In-country Mexican migration of pregnant women to Tijuana from 2007 to 2008.

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Table 1.

Demographic and Clinical Characteristics among Labor and Prenatal Patients, by Migration Status from 2007 to 2008.

	Tijuana (n = 2502), N (%)	Migrant (n = 829), N (%)	P Value
Mean age, years	23.4	22.7	.005
Mean gestation	2.3	2.08	<.001
Mean parity	0.95	0.79	.002
Prenatal care visits	4.02	3.85	.09
Gestational age (at PNC visit), weeks	34.2	34.1	.73
Enrolled, n (%)
Labor	1040 (41.6)	328 (39.6)	.31
Prenatal care	1462 (58.4)	501 (60.4)
Maternal lifetime risk factors
Transfusion	82 (3.3)	34 (4.1)	.26
Injection drug use	44 (1.8)	15 (1.8)	.93
Methamphetamine use	137 (5.6)	24 (2.9)	.003
Other drugs	76 (3.3)	14 (1.8)	.035
Homeless	22 (0.9)	5 (0.6)	.44
Commercial sex	17 (0.7)	6 (0.7)	.91
Ever in jail	44 (1.8)	12 (1.5)	.54
STI	60 (2.5)	35 (4.5)	.006
Age at sexual debut, years	16.7	17.2	<.001
Spouse lifetime risk factors
Injection drug use	88 (3.8)	27 (3.6)	.77
Methamphetamine use	236 (10.4)	48 (6.6)	.002
Ever in jail	230 (9.6)	65 (8.2)	.23

Abbreviations: PNC, prenatal care; STI, sexually transmitted infection.

Discussion

This study documented a high Mexican internal migration of women of childbearing age to Tijuana, Baja California. In addition, among women accessing prenatal care or admitted to the delivery unit at Tijuana General Hospital, 71% were either migrants or were born outside of Tijuana, reflecting the highly mobile status of the population accessing care at Tijuana General Hospital. Furthermore, we consistently documented a very high HIV prevalence among pregnant women in Tijuana than among other Mexican localities, regardless of their migration status. ¹¹ Similar to our previous study, we found Tijuana residents to be more likely than migrants to engage in HIV acquisition high-risk behaviors. ¹¹ Our study expands on our previous observation and quantifies the female migrant population, mostly coming from south, central Mexico and from western states. Interestingly, among the long-term Tijuana residents who were born elsewhere, the birth states mostly represented are the same as the migrant states, namely Chiapas, Sinaloa, Jalisco, Veracruz, Michoacan, and Nayarit.

Population migration has been linked to HIV acquisition risk behaviors in sub-Saharan Africa, ^6,16 Asia, ⁷ and Latin America. ¹⁷ Social isolation, gender inequalities where women are often forced to have survival sex, violence, and human rights violations are linked to HIV acquisition risk behaviors among migrant populations. ¹⁷ Studies on the effects of Mexican migration on HIV prevalence had been conducted among certain populations at high risk, such as injector drug users in Tijuana, ¹⁸ female sex workers who inject drugs in Tijuana and Ciudad Juarez, ¹⁹ and deported predominately male labor Mexican migrants. ¹⁰ A study conducted in 5 Mexican states, Jalisco, Michoacan, Mexico State, Oaxaca, and Zacatecas, among a predominately male population found more HIV acquisition risk behaviors (multiple sexual partners and illicit drug use) among migrants who returned from the United States than among nonmigrants, although no HIV testing was conducted. ⁸ In our study, women who were long-term Tijuana residents had a younger age at sexual debut, higher methamphetamine use, and had a spouse who used methamphetamine more often than the recent migrants.

Since most long-term Tijuana residents were born elsewhere in Mexico, it is conceivable that high-risk behavior was adopted after residing in Tijuana for over 5 years. A limitation of our study is that it is hospital based, conducted among pregnant women, and in a low-income population; therefore, these findings may not be generalizable to the broader female population of Tijuana or Baja California. However, similar effects have been seen among male Mexican migrants in California, among whom HIV acquisition risk behavior such as having sex while under the influence of drugs or alcohol, sex with a commercial sex worker, or sex with men were more pronounced among migrants with more than 5 years of residence in California compared to the same risk behaviors prior to migration. ²⁰ A study among 157 female injection drug users in Tijuana had similar findings, with 65% being born outside Baja California and long-term Tijuana residents were more likely to be HIV infected. ¹⁸ In our study, while investigating HIV acquisition risk behaviors, first presentation at the labor and delivery unit was independently associated with HIV infection on multivariate regression analysis. This association was previously described at Tijuana General Hospital, ¹² which is a reflection of the high-risk population not accessing prenatal care for which the first medical encounter is at the labor and delivery unit. Our study among pregnant women documents a high HIV prevalence and frequent HIV acquisition risk behaviors among both long-term Tijuana residents and recent migrants.