- The step-ladder fever pattern is a characteristic clinical feature of typhoid fever, caused by Salmonella typhi.
- This pattern describes a gradual, progressive rise in temperature over several days, reflecting the multiplication of the organism and the host's inflammatory response.
- Early in the illness, fever is low-grade, then increases step-wise to high temperatures as the bacteria invade the reticuloendothelial system.
- This contrasts with the intermittent fevers seen in malaria or the biphasic fever of dengue.
- Hence, the presence of a step-ladder fever is a useful clinical clue in diagnosing typhoid fever.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Typhoid and Paratyphoid Fevers, Page 785.