The incidence of tuberculosis (TB) in the U.S. is reported as being on the decrease, however untreated infected people act as a reservoir for disease. Any pool of the world's population harboring this disease gives cause for concern, especially since the BCG vaccine is only 70 percent to 80 percent effective at best.
New research published in BMC Public Health shows that in 2009 the number of cases of TB reported across America was much lower than that recorded in previous years. This larger than expected decrease was most noticeable among recent immigrants, the homeless and other disadvantaged groups, which suggested that the decrease was most likely due to economic recession and lower immigration rates and may mask the future impact of TB.
According to the World Health Organisation it is estimated that as much as a third of the world's population is currently infected with TB, and this is still increasing across Africa and South East Asia. The U.S. National Tuberculosis Surveillance System (NTSS) has shown that, over the 10-year period from January 2000, there has been a year on year decrease of 3.8 percent in the rate of cases, but in 2009 this dropped to 11.4 percent. Toward the end of 2009 the rate began to return to normal.
A multicentre team led by Dr. Carla Winston from the Centers for Disease Control and Prevention (CDC) analyzed the NTSS data in conjunction with patient information and changes in reporting procedure. They found that the biggest decrease in reported cases occurred for the group of people who were foreign born and had moved to America in the last two years, and amongst the US-born homeless or drug users. This drop was not related to under-reporting of TB cases, or to improvements in TB control, nor had there been any alteration in the transmission rate of TB.
The researchers hypothesized that the decline could be due to economic recession. TB is usually curable but takes a six-to-nine month course of antibiotics. The authors suggested that during a recession prospective patients may be worried about the cost of a long treatment plan and therefore be less likely to come forward and be treated. An additional factor may be the decrease in immigration seen during the economic downturn. Regardless of recession, eventually people with TB are going to need medical care and, due to the delay in seeking help, their disease may be more severe, more infectious, and more resistant to treatment.