In Tijuana it was 5.7 percent. Rates of drug use among the participants in the study were much higher than what has been found in household surveys in the two countries.
The researchers also found that Los Angeles patients born in Mexico were twice as likely, and Los Angeles patients born in the United States were six times more likely, of being moderate-to-high drug users compared with Tijuana patients born in Mexico.
High Rate of Drug Use Was Surprising
The findings of high rates of drug use ran counter to assumptions, said Dr. Lillian Gelberg, the study's lead investigator and a professor of family medicine at the David Geffen School of Medicine at UCLA.
"Prevailing expectations were that alcohol would be the major problem and drug use would be lower,'' said Gelberg, who is also a professor of health policy and management at the UCLA Fielding School of Public Health. "But what we found was that the rate of problem drug use -- that is, moderate-to-high use -- was very similar to problem alcohol use."
Moderate-to-high alcohol use was 15.2 percent in East Los Angeles compared to 6.5 percent in Tijuana. Moderate-to high tobacco use was 20.4 percent in East Los Angeles and 16.2 percent in Tijuana.
Drug Screening Should Be Routine
While drug use was higher in Los Angeles than it was in Tijuana, the rates in both cities are high enough that screening for drug, alcohol and tobacco use should be integrated into routine primary care in community clinics on both sides of the border, said Melvin Rico, clinical research coordinator in the UCLA Department of Family Medicine who served as the field research coordinator for the study.
"Being able to reach a vulnerable population while waiting for a doctor is, I think, very important," Rico said.
The paper is part of a larger study of an intervention that found a few minutes of counseling in a primary care setting could steer people away from risky drug use and full-fledged addiction.
Self-Reported Substance Abuse
For this study, which ran from March 2013 through October 2013, the researchers recruited 2,507 adults in Los Angeles and 2,890 in Tijuana who were eligible for the World Health Organization's Alcohol, Smoking and Substance Involvement Screening Test. The researchers designed a simple tool that allowed participants to anonymously self-report substance abuse on a computer tablet with a touch screen. Given the stigma associated with drug use, the researchers wanted to remain sensitive to people's fears of privacy in a way that still encouraged them to be truthful about their substance use.
Questions about substance use were combined with others about healthy eating, exercise, and chronic illnesses so that the patients would not feel stigmatized about a particular behavior, Gelberg said.
Quiz Adapted for Cultural Differences
"We aren't using interviews and the patients are filling it in on their own," she said. "We developed this program so that it would work even for patients of low-literacy levels, asking one question at a time and allowing for an audio option with headsets according to patient's preference. For instance, it would ask 'did you use cocaine in the last three months and a 'yes' or 'no' would light up on the computer screen.'"
The tool could also easily switch between English and Spanish and the questions and approach were adapted to Latinos in Mexico, whose culture and characteristics had differences compared to those in Los Angeles.
Results Subject to Under-Reporting
Participants took the survey while they were in the clinic waiting room, and it took very little time -- a mean of 1.3 minutes in Tijuana and 4.2 minutes in Los Angeles.
This tool can be of use in a primary care clinic because people generally don't volunteer their drug use to their doctors, who for their part don't know how to broach the subject, Gelberg said.
The study has some limitations. Substance use was based on patient self-reporting, which could make the findings subject to under-reporting. Also, the findings may or may not be the same in health care settings other than community health centers or in other cities in the United States and Mexico.