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Most fungi that pathogenically affect humans live in soil. If a person is not healthy, has an open wound, or is immunocompromised, a fungal infection can be very aggressive.
For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
Children of people with alcoholism are more inclined to drink alcohol or use hard drugs. In fact, they are 400 times more likely to use hard drugs than those who do not have a family history of alcohol addiction.
Since 1988, the CDC has reported a 99% reduction in bacterial meningitis caused by Haemophilus influenzae, due to the introduction of the vaccine against it.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.