Hand, Foot, and Mouth Disease and Risk Factors

Hand, foot, and mouth disease is a relatively common acute viral illness, as its name suggests, in which blisters appear in the mouth, hands, and feet. Because the symptoms are so characteristic, it can often be identified visually, but sometimes it is difficult to recognize when the number of blisters on the hands and feet is very small, or when ordinary small red rashes appear instead of blisters.

This disease occurs when an "enterovirus" enters the body. In most cases, the symptoms are mild, with either no fever or only a slight fever. Blisters in the mouth burst and form ulcers, and because it hurts to eat when this happens, food intake temporarily decreases before the illness naturally improves. However, in some cases, a person may be unable to eat at all, leading to dehydration, or neurological complications such as meningitis or encephalitis may occur, requiring hospitalization. In extremely rare cases, it can be fatal, so caution is needed.

Hand, foot, and mouth disease is an exanthematous illness caused by infection with an "enterovirus" that produces characteristic blisters or red rashes on the mouth, hands, and feet.

Causes and Risk Factors

1. Causative viruses

Hand, foot, and mouth disease is caused by infection with an "enterovirus." Enteroviruses are divided into "polioviruses," "cox­sackieviruses," "echoviruses," and "other enteroviruses," and most cases are caused by "cox­sackieviruses." Coxsackieviruses are further classified into groups A and B according to serotype, and each group is again divided into dozens of viruses according to their properties and identified by number.

The most common virus that causes hand, foot, and mouth disease is "Coxsackievirus A16," and it can also be caused by "Coxsackievirus A5, A7, A9, A10, B2, B5," and others. Hand, foot, and mouth disease caused by "enterovirus 71," which circulated in Korea from 2009 to 2013 and previously caused outbreaks in Taiwan and China, is characterized by a worse prognosis than infections caused by other viruses, with more frequent neurological complications such as encephalitis that can also lead to death.

Enteroviruses, including coxsackieviruses, are resistant in everyday temperatures and cannot survive only at temperatures above 50˚C; they can survive at refrigerator temperatures. They are also not disinfected by lipid solvents such as alcohol.

2. How the disease develops

Viral disease begins when a patient’s stool containing the virus gets on the hands or on everyday objects (such as items the patient touches) and enters the mouth, or when the patient’s respiratory secretions or saliva enter the mouth, or through direct contact with fluid from blisters in the mouth or on the skin. After infection, the virus may be shed in the stool for weeks to months, and it may remain infectious in respiratory secretions for 1 to 3 weeks. The virus can also be shed even when there are no symptoms. Its infectivity is moderate among infectious diseases, lower than chickenpox or measles.

As with all infectious diseases, hand, foot, and mouth disease also requires a relatively large number of viruses to enter the body in order to develop; being exposed to just one or two viruses does not necessarily cause illness. This is similar to how not everyone who comes into contact with a person with a cold catches a cold, but only some do. Therefore, washing hands and thoroughly cleaning everyday objects that may have been contaminated with the virus to reduce the number of viruses is a very effective way to prevent hand, foot, and mouth disease.

Because enteroviruses can survive in the surrounding environment, infection can occasionally occur by drinking water containing the virus or even in swimming pools, but most infections occur in environments where patients may be present, such as homes, childcare facilities, playgrounds, and summer camps—places where many children gather.

Most enteroviruses, including coxsackieviruses that cause hand, foot, and mouth disease, have a similar mechanism for causing illness. After entering through the mouth, the virus multiplies in the mucosa of the throat or intestines, and the multiplied virus is shed in the stool or upper respiratory secretions even before symptoms appear. The incubation period from the first entry of the virus into the body until symptoms appear is on average 3 to 10 days. During this time, the virus that has entered the body moves to lymphoid tissue and multiplies to a level sufficient to cause symptoms. After that, the virus enters the bloodstream, causing symptoms such as fever and fatigue. The virus that enters through the blood goes to the spleen, liver, and bone marrow, then spreads again to each target organ, where it multiplies and causes full-blown symptoms. The disease that appears differs depending on the target organ the virus spreads to: in hand, foot, and mouth disease the target organ is the skin; in meningitis it is the meninges surrounding the brain; and in myocarditis it is the heart.

3. Outbreak period and risk factors

Hand, foot, and mouth disease generally spreads from summer to early autumn, but the outbreak period varies each year. In Korea, according to laboratory sentinel surveillance by the National Institute of Health and voluntary sentinel surveillance centered on private pediatric and adolescent clinics, outbreaks in 2014 and 2015 began around April and continued until December. In 2016, it showed a pattern of beginning around April. During outbreak periods, cases occur in clusters mainly in infant and childcare facilities, and the number of cases also increases within the same community.

The age group most susceptible to the disease is under 10 years old, especially under 5 years old. During outbreak periods, adolescents and adults who have never had the disease can also become infected through close contact within the family with a child patient. The rate of infection is generally the same regardless of sex.

So far, this has been an explanation of hand, foot, and mouth disease and its risk factors.

In the next part, we will look at the symptoms and complications of hand, foot, and mouth disease.

Source: Korea Centers for Disease Control and Prevention, National Health Information Portal