Foreign-borns account for 39% of 1997 cases
New prophylaxis guidelines due out this summer
With 39.4% of TB cases in the United States now occurring among the foreign-born, clinicians all over the country are having to make adjustments.
TB among the foreign-born is no longer strictly a bi-coastal phenomenon, says Nancy Binkin, MD, MPH, associate director for international activities at the Division of Tuberculosis Elimination at the The Centers for Disease Control and Prevention (CDC).
True, two-thirds of foreign-born cases still occur in just eight states, she adds. But even there, case totals have been affected by the recent shift. In California, for example, the foreign-borns make up 70% of all cases.
Meanwhile, in many heartland states, absolute case numbers may still be low, but the proportion of foreign-born cases has risen strikingly.
What's actually happened is the result of two separate trends, says Binkin. Since 1986, the first year the CDC started collecting data on place of birth, cases among the foreign-born have risen steadily. But for the past two years, foreign-born cases have leveled off. Over the same two years, cases of home-grown TB have fallen, by 6% to 7% each year. The result of the two trends has been a substantial increase of the proportion of foreign-born cases, says Binkin.
Should TB controllers be worried?
If present trends hold, America is poised to join a number of other developed countries - Australia, Canada, several countries in Western Europe, and the Netherlands - where the foreign-born make up the majority of TB cases, says Binkin.
What, exactly, does this mean for TB controllers? For one thing, it creates a huge pool of people latently infected with TB, says Binkin. Of the estimated 24 million foreign-born people in the United States (one in 11), conservative estimates put the number of infected people at about eight million, or a third of the total, Binkin says.
Since many of these infections are remote, not recent, the risk for reactivation among the foreign-born is relatively low - somewhere between 2% and 3%, she adds. But that's still a lot of people; and since not all eight million of the infected foreign-born can be placed on isoniazid prophylaxis, who should get top priority?
Decisions about which subgroups should get priority must take into consideration factors such as country of origin, age, and time of arrival in the United States, says Binkin.
For example, more recent arrivals are more likely to develop TB, since the longer people are removed from an environment where they're exposed, the smaller their risk. As for native country, someone from Western Europe obviously falls into a lower-priority group than someone from Southeast Asia.
These and other points will be discussed in the new CDC recommendations on prophylaxis for the foreign-born that are due out sometime this summer, Binkin says, probably as a supplement to Morbidity and Mortality Weekly Report.
Along with decisions about who gets prophylaxis for latent infection, there are other repercussions, too.
A study recently conducted in Seattle looked at contact investigations among the foreign-born and found these two differences, says Binkin:
1. Contacts of foreign-born cases are likely to be more numerous than contacts of homegrown cases.
2. Foreign-born contacts are more likely to be skin-test positive.
This means the tuberculin skin test is much less accurate in defining infection in these groups, since often they've either already been infected, they've had BCG vaccinations, or both, says Dick Menzies, MD, director of the Montreal Chest Clinic.
Some cultures equate TB with shame, fear
He points to other effects, too. In Montreal, with its sizeable community of Haitians and Filipinos, TB controllers have to address the widespread belief among Haitians that equates TB with a death sentence; and with the Filipino sense that TB is a shameful diagnosis to be kept hidden, somewhat like a venereal disease, Menzies says.
Providing directly observed therapy to Montreal's immigrant population, many of whom hold non-unionized jobs, is tougher, too, since workers sometimes worry more about their jobs than their health, he adds.
Canada is studying its immigration screening procedures to see how effective they are, Menzies says.
Perhaps Canadian dollars would be better spent by investing them in TB control in the countries that supply the country with its immigrants and refugees, he adds. "It's as if you're turning off the tap instead of just constantly mopping the floor," he says.
Along those lines, the CDC is already working to improve TB control programs in countries that act as supply lines for large numbers of people, says Binkin. In Mexico, the top supplier of foreign-born U.S. cases (at 25% of the total) and Vietnam (providing 11%, in third place after the Philippines), the CDC has established various collaborative programs.
In Mexico, for example, the United States provides laboratory support and training along the border. Partly as a result of projects aimed at helping Mexico survey for drug resistance, Mexico has switched from a three-drug regimen to a more appropriate four-drug regimen, says Binkin.
In Vietnam, a three-way partnership (among the Dutch, the Vietnamese, and Americans) is going particularly well, says Binkin.
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