Hand foot and mouth disease (HFMD) is caused by certain members from a group of viruses known as enteroviruses (tiny viruses composed of ribonucleic acid [RNA] and protein). Viruses included in the enterovirus group include coxsackie viruses, polioviruses and echoviruses. Infection with coxsackievirus A16 is the most frequent cause of HFMD. Other strains of coxsackievirus A and enterovirus 71 are also common causes of HFMD.

Epidemic HFMD viral infections are usually caused by specific types of enteroviruses. Infections usually occur as isolated events, but epidemics occur fairly regularly, approximately every 3 years. Cases of HFMD occur most often in the summer and early fall.

HFMD is very contagious and spreads through direct contact with the bodily fluids (e.g., saliva, nasal and throat discharge), fluid from the blistering skin sores and feces (stool) of an infected person. The virus can also spread when an infected person coughs or sneezes, spraying a mist of fluid containing viruses in the air.

Once the virus enters the body, usually via the mouth, it reproduces in the digestive tract. At this stage, the immune system normally prevents the infection from spreading, resulting in few or no symptoms. When the immune system is not successful in attacking the virus, it can survive and spread into the bloodstream, resulting in HFMD.

The usual incubation period (amount of time from infection to onset of symptoms) is between three to six days. A person is most contagious during the first week of the illness. However, HFMD is generally mild and nearly all patients recover without medical treatment in seven to 10 days.

People who have developed HFMD become immune to the virus that caused it. However, this does not mean they will not develop the condition again. It is possible to develop subsequent episodes of HFMD if a different member of the enterovirus group enters the body.

HFMD most commonly affects children and can spread rapidly wherever groups of children are in close contact, such as in schools and childcare settings. Although it can also affect adults, children are at increased risk for HFMD because their immune systems have not yet fully developed. They are also less likely than adults to have developed immunity as a result of previous exposure.

Additional risk factors for developing HFMD include:

• Direct contact with a person who has the disease or with contaminated surfaces or objects (e.g., utensils).
  
  
• Weakened immune system. People suffering from diseases that weaken the immune system, such as diabetes (high blood sugar levels), may be more prone to infection.
  
  
• Crowded conditions, especially in places where there is poor hygiene.