document: Black Americans suffer six times more tuberculosis than whites do , and one important reason appears to be a genetic susceptibility to the disease , according to a study today . The research found that when living conditions are identical , black people are twice as likely as whites to get infected with the TB bacteria . The relatively high rate of TB among blacks has traditionally been blamed on crowded housing and other conditions of poverty . While social factors undoubtedly play a central role , the study suggests that innate susceptibility also contributes . `` We found that there is a systemic difference between whites and blacks , '' said Dr. William W. Stead . `` Whites seem to be more able to fend off the organism without it 's ever being able to establish an infection . '' Stead , a tuberculosis specialist at the Arkansas Department of Health , discovered the racial difference while analyzing health statistics from nursing homes and prisons . `` It 's a very intriguing finding , '' commented Dr. George Comstock of Johns Hopkins University . `` I never quite believe anything until somebody replicates it . But I do n't know of any real holes in this one . '' At the National Institute of Allergy and Infectious Diseases , Dr. George Curlin called the findings `` plausible and provocative . '' However , he added : `` I 'm scared to death that people are going to say this explains it all and forget everything else . Of the total six times difference , what proportion is attributable to biology and what to social factors ? I would say that biology is relatively minor . '' Stead 's study , published in the New England Journal of Medicine , was based largely on a review of 25,398 elderly people who were free of TB infection when they were admitted to Arkansas nursing homes . When they were retested at least two months later , 14 percent of blacks and 7 percent of whites showed evidence of new infections . Prison data from Arkansas and Minnesota also found that black inmates were twice as likely as white prisoners to catch the bacteria while incarcerated . Another soon-to-be published study reports the discovery of a racial difference in the way blood cells respond to the TB bacteria , which could help explain why blacks seem to be more prone to tuberculosis . About 22,000 cases of tuberculosis are reported annually in the United States , resulting in 1,700 deaths . In the population at large , tuberculosis is about six times as common among blacks as whites . An estimated 10 million Americans are believed to be infected with the bacteria but not sick . The disease , which attacks the lungs , has long been associated with poor , crowded living conditions . Stead 's study found that blacks got infected more readily than whites , regardless of the race of the person who initially brought the infection into the nursing home . In homes where the initial source of the disease was white , 17 percent of blacks and 12 percent of whites caught the infection . When the primary source was black , 12 percent of blacks and 8 percent of whites contracted the bacteria . This phase of the study also suggests , however , that infected whites are more potent spreaders of the infection than are blacks . Stead speculated that whites have evolved better defenses against TB , because the bacteria has long been common in Europe and parts of Africa north of the Sahara , but is traditionally rare in sub-Saharan Africa . By contrast , blacks are genetically more resistant than whites to malaria , which is common in Africa . In the other study , Dr. Alfred Crowle of Webb-Waring Lung Institute at the University of Colorado found differences in the resistance of germ-eating blood cells called macrophages . In blacks , these cells are more likely to harbor TB infections . `` This helps explain why black people are more susceptible to tuberculosis than are white people , '' said Crowle . At the turn of the century , TB was the nation 's leading cause of death . The number of cases fell steadily in recent decades until 1984 . Experts believe the decline has leveled off in part because of the emergence of the AIDS virus , which weaken the body 's resistance to TB bacteria . Others possible factors include homelessness and immigration of people from areas where the disease is still common .
extractive_keyphrases: tuberculosis black americans whites infectious diseases tb bacteria racial difference