Paratyphoid fever, also known simply as paratyphoid, is a bacterial infection caused by one of three types of Salmonella enterica. Symptoms usually begin 6–30 days after exposure and are the same as those of typhoid fever. Often, a gradual onset of a high fever occurs over several days. Weakness, loss of appetite, and headaches also commonly occur. Some people develop a skin rash with rose-colored spots. Without treatment, symptoms may last weeks or months. Other people may carry the bacteria without being affected; however, they are still able to spread the disease to others. Typhoid and paratyphoid are of similar severity. Paratyphoid and typhoid fever are types of enteric fever.

Paratyphoid is caused by the bacterium Salmonella enterica of the serotypes Paratyphi A, Paratyphi B, or Paratyphi C growing in the intestines and blood. They are usually spread by eating or drinking food or water contaminated with the feces of an infected person. They may occur when a person who prepares food is infected. Risk factors include poor sanitation as is found among poor crowded populations. Occasionally, they may be transmitted by sex. Humans are the only animals infected. Diagnosis may be based on symptoms and confirmed by either culturing the bacteria or detecting the bacterial DNA in the blood, stool, or bone marrow. Culturing the bacteria can be difficult. Bone-marrow testing is the most accurate. Symptoms are similar to those of many other infectious diseases. Typhus is a different disease.

While no vaccine is available specifically for paratyphoid, the typhoid vaccine may provide some benefit. Prevention includes drinking clean water, better sanitation, and better handwashing. Treatment of the disease is with antibiotics such as azithromycin. Resistance to a number of other previously effective antibiotics is common.

Paratyphoid affects about six million people a year. It is most common in parts of Asia and rare in the developed world. Most cases are due to Paratyphi A rather than Paratyphi B or C. In 2015, paratyphoid fever resulted in about 29,200 deaths, down from 63,000 deaths in 1990. The risk of death is between 10% and 15% without treatment, while with treatment, it may be less than 1%.