Typhoid fever, a disease that causes headaches,
digestive upset, and a high fever, is caused by the
bacterium Salmonella typhi. Typhoid can be
spread from person to person by contaminated
water or food or by a lack of cleanliness. Since
the 19th century, the number of individuals
infected with this disease has decreased. Which
statement best explains why the number of
people with this disease and other bacterial
diseases has decreased over the last 100 years?
(1) Scientists have corrected the damaged genes
that cause typhoid fever and other infectious
diseases.
(2) Public health officials have placed better
controls on the use of the toxic substances
that cause these diseases.
(3) Typhoid fever, like most other bacterial
diseases, is often caused by a lack of proper
nutrition.
(4) Personal habits, such as hand washing, have
greatly reduced contamination from bacteria.