Risk to U. S. citizens immeasurable.

Foreign-born persons entering the U.S. legally must go through a health screening process. They must be evaluated for TB and certain other diseases before arriving on U.S. soil. People entering illegally, however, obviously bypass this safeguard to U.S. public health.

U.S. border authorities are responsible for intercepting illegal immigrants entering from Mexico. The Centers for Disease Control and Prevention (CDC) monitors the potential for a more deadly invasion: infectious diseases being carried by undocumented aliens.

CDC Border Infectious Disease Surveillance (BIDS)

Through its Border Infectious Disease Surveillance (BIDS) project, which the CDC began organizing in 1997 in collaboration with Mexican health officials, the agency identified hundreds of persons with hepatitis or a febrile exanthem. The CDC has also observed that "immigrant women may be at risk for diseases such as rubella (due to lack of vaccination) or listeriosis (due to food preparation practices)."

Tuberculosis (TB) is a major threat. The CDC cites foreign-born persons as one of the groups at high-risk for tuberculosis (TB). In 2003, says the agency, foreign-born persons accounted for 94 percent of TB cases among Asians and 74 percent of cases among Hispanics, and six states (California, Florida, Georgia, Illinois, New York, and Texas) collectively accounted for 57 percent of the national total number of TB cases.

Moreover, reports the agency, low socioeconomic status--measured by crowding, education, income, poverty, public assistance, and unemployment (with crowding having the greatest impact)--is associated with an increased risk for TB.

The CDC reports that persons born outside the United States accounted for 53 percent of reported TB cases in 2003, and of the five countries of origin that accounted for the greatest number of foreign-born persons with TB, Mexico had the most (26 percent).

The CDC reports that during 1992-2002, an estimated 380,000-536,000 persons entered the U.S. each year as legal immigrants, refugees, or asylees. "In 2002, among the estimated 516,000 persons in those categories, 86.6 percent were from countries with high incidence of TB."

The CDC says that in Mexico's six border states, "estimated annual TB incidence is 27.1 cases/100,000 population, compared with 5.1 cases/100,000 population in the United States. In 1999, Mexico was the country of origin for 23% of foreign-born persons in the United States with reported TB, and 75% of those cases were reported from the four U.S. border states. In 1996, those same states reported 83% of TB cases among foreign-born Hispanics. The high rate of TB at the border, the substantial number of border crossings, the substantial geographic area involved, and the prevalent cultural and linguistic barriers make TB control a challenge in this region."

In addition to TB, Mexico and Central America are known to harbor malaria, yellow fever, food and waterborne diseases, dengue, filariasis, leishmaniasis, onchocerciasis, american trypanosomiasis, and myiasis, according to NBC4.com's CDC-based map of the world's exotic diseases.

Who's responsible for stopping diseases at the U.S. border?

The Secretary of the Department of Health and Human Services has statutory responsibility for preventing the introduction, transmission, and spread of communicable diseases in the United States. The Secretary of the Department of Health and Human Services, according to Titles 8 and 42 of the U.S. Code and applicable regulations.

Specifically, the Division of Global Migration and Quarantine works through a variety of activities to prevent the introduction, transmission, and spread of communicable diseases in the United States. It operates Quarantine Stations at ports of entry, establishes standards for medical examination of persons headed legally for the United States, and administers interstate and foreign quarantine regulations governing the international and interstate movement of humans, animals, and cargo.

As the CDC's BIDS project demonstrates, diseases don't recognize national borders. Even though the U.S. has laws and practices in place to catch infectious diseases hiding in the bodies of persons entering this country, the effectiveness of those laws and practices suffers when people enter illegally.