Infectious diseases are caused by infection of organism with pathogenic agents, which may lead to epidemics. Many infectious diseases such as syphilis, diphtheria, measles, and acquired immunodeficiency syndrome have specific and non-specific manifestations in the oral cavity. However, the same disease may have different oral manifestations in different patients clinically. We can apply the strategy of "three unusuals and one change" in clinical reasoning for diagnosis of infectious diseases with oral manifestations. The so-called "three unusuals" refer to unusual age, unusual location and unusual effect, and "one change" means the change from rare to common. In this article, we will give a comprehensive introduction about the oral manifestations of common communicable diseases and their diagnostic strategies.
Keywords: Diagnosis; Differential diagnosis; Infectious diseases; Oral diseases; Oral manifestations.