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.