Chloramphenicol is used for treating typhoid fever due to its effectiveness against the bacteria Salmonella enterica serotype Typhi, which causes the disease. Here are some reasons why it is used:

1. Broad-spectrum Antibiotic: Chloramphenicol has a broad spectrum of activity and can target a wide range of bacteria, including Salmonella Typhi.
2. Bacteriostatic Action: It works by inhibiting bacterial protein synthesis, effectively stopping the growth and reproduction of bacteria. This helps the immune system to overcome the infection.
3. Penetration: Chloramphenicol can penetrate tissues and reach the bloodstream effectively, which is crucial for treating systemic infections like typhoid fever.
4. Historical Effectiveness: Historically, chloramphenicol was one of the first antibiotics found to be highly effective against typhoid fever, and it significantly reduced the mortality rate of the disease when it was first introduced.

However, it is worth noting that the use of chloramphenicol has declined due to the emergence of antibiotic-resistant strains of Salmonella Typhi and the potential for serious side effects, such as bone marrow suppression leading to aplastic anemia. In many regions, other antibiotics, such as ciprofloxacin, azithromycin, and third-generation cephalosporins, are now preferred for treating typhoid fever.