There are usually intermediate steps, sometimes many of them. Among the more common causes are:

• water that has come in contact with feces and is then inadequately treated before drinking;
• food that has been handled with feces present;
• poor sewage treatment;
• poor or absent cleaning after handling feces or anything that has been in contact with feces.
• some sexual practices — such as anilingus, coprophilia, and ass to mouth

Some of the diseases that can be passed via the fecal-oral route include:

• Giardiasis
• Hepatitis A
• Hepatitis E
• Rotavirus
• Shigellosis (bacillary dysentery)
• Typhoid fever
• Vibrio parahaemolyticus infections
• Enteroviruses, including poliomyelitis
• Cholera

References