The most important exception is pregnancy. Unlike many other infections, TB is not passed on by contact with a patient's clothing, bed linens, or dishes and cooking utensils. Of course, if a severely infected patient emits huge numbers of bacilli, the chance of transmitting infection is much greater. As a rule, close, frequent, or prolonged contact is needed to spread the disease. Only about one in three close contacts of a TB patient, and fewer than 15% of more remote contacts, are likely to become infected. Tuberculosis is not, however, highly contagious compared to some other infectious diseases. This mist, or aerosol as it is often called, can be taken into the nasal passages and lungs of a susceptible person nearby. This type of transmission means that when a TB patient exhales, coughs, or sneezes, tiny droplets of fluid containing tubercle bacilli are released into the air. Tuberculosis spreads by droplet infection. There still are an estimated 8-10 million new cases of TB each year worldwide, causing roughly 3 million deaths. AIDS patients are much more likely to develop tuberculosis because of their weakened immune systems. An additional factor is the AIDS epidemic. Infected visitors and immigrants to the United Stateshave also contributed to the resurgence of TB. This upsurge was in part again a result of overcrowding and unsanitary conditions in the poor areas of large cities, prisons, and homeless shelters. Although other more effective anti-tuberculosis drugs were developed in the following decades, the number of cases of TB in the United States began to rise again in the mid-1980s. tuberculosis, was discovered in the early 1940s, the infection began to come under control. ![]() When streptomycin, the first antibiotic effective against M. ![]() The disease became widespread somewhat later in the United States, because the movement of the population to large cities made overcrowded housing so common. Tuberculosis spread much more widely in Europe when the industrial revolution began in the late nineteenth century.
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