In the mid-seventeenth and eighteenth centuries, many countries underwent an Industrial Revolution. Because of inventions such as the steam engine, cities saw an increase of factory and industrial jobs, and more and more people moved from farms in the country to work in the city. Once there, workers often lived in very close contact with relatives and neighbors. Under those crowded and unsanitary conditions, tuberculosis was able to spread easily among the population.

Before scientists knew what caused tuberculosis, the disease was commonly referred to as consumption.

Until recently, there was no way of treating the disease. Instead, people with "consumption" were isolated in private hospitals or sanitariums. The purpose of isolation was to prevent the disease from spreading to uninfected people. Because of this practice, the study of tuberculosis also became separated from other fields of medicines. Entire organizations were created to study the disease, its effects on patients, and its impact on society as a whole.

In 1885 the German microbiologist Robert Koch discovered the tubercle bacillus and showed that this microorganism was responsible for tuberculosis. At the time, TB was responsible for one out of every seven deaths that occurred in Europe.

At the turn of the twentieth century, more than 80 percent of all Americans had been infected with TB before the age of twenty. Most of these people did not become ill since their bodies were able to fight off the disease. However, tuberculosis was still the most common cause of death among Americans. Even as late as 1938 there were more than seven hundred TB hospitals in the United States.

The first step in the conquest of TB occurred with the discovery of streptomycin in the early 1940s. Streptomycin is an antibiotic that kills the tubercle bacillus. Eventually, a number of other anti-tuberculosisdrugs were developed and progress was made in overcoming the disease.

By 1985 a conference was held to develop plans to eliminate tuberculosis forever. The number of cases of TB had been dropping for many years and many experts thought that TB was no longer going to be a serious disease. Then, in the late 1980s, the number of TB cases began to rise, both in the United States and around the world. Why did this change come about? At least five factors are thought to play a role in the return of TB as a major health problem:

• Education. Efforts to educate people about the disease may have lessened as the perceived threat of TB decreased.
• AIDS/HIV epidemic. As HIV weakens a person's immune system, a patient can become more prone to developing infectious diseases, such as tuberculosis.
• Living conditions. People who are poor, or homeless, or who live in crowded and unsanitary conditions may also develop weakened immune systems, or increase their chances of coming in contact with the disease. Drug users often have weakened immune systems as well. As the number of people in these categories increases, so does the rate of tuberculosis.
• Population movement. The increased movement of people across national boundaries is another factor. When people take vacations, conduct business, or move to new countries, they may take TB with them.
• Drug Resistance. TB bacteria have become resistant to many of the drugs once used to treat the disease.

Experts estimate that eight to ten million new cases of tuberculosis develop worldwide every year. The disease is thought to be responsible for about three million deaths annually. While there are various ways to fight the disease, if root problems, such as homelessness, poverty, drug use, and drug resistance are not solved, tuberculosis may once again become a major health problem.