Hepatitis A cases surge with younger generations at high risk of infection

THERE has been a significant increase of Hepatitis A infection in Thailand this year with most Thais under 40 years of age lacking immunity and the outbreak originating from migrant workers and contaminated food and water, PPTVHD36 quoted Dr. Yong Poovorawan, head of the Centre of Excellence in Clinical Virology at the Faculty of Medicine, Chulalongkorn University, as saying today (April 27).

Hepatitis A is caused by an enterovirus and is transmitted through fecal contamination in the environment, including food and drinking water, potentially leading to major outbreaks.

Although Hepatitis A has multiple genotypes, there is only one serotype, meaning it is a once-in-a-lifetime infection with lifelong immunity. The virus is highly contagious, and currently, the majority of the Thai population under 40 years old lack immunity and are unvaccinated. Approximately 50 percent of the population aged 40-50 years already have immunity, and those over 60 years old mostly have immunity from natural infection, Dr. Yong said.

“Modern hygiene regarding food and drinking water is much better than in the past, so younger generations lack immunity and therefore need vaccination. 

“Alternatively, it could be said that anyone born in an era where people shared water from the same bowl likely already has immunity – those born 50 or 60 years ago. If you ask if you ever shared water from a bowl, it will reveal your age. If you lived in that era, you would mostly have immunity and wouldn’t need vaccination. 

“Most outbreaks typically occur at the beginning of the rainy season, but this year it started in the summer, which is worrying as it suggests a likely increase in cases during the rainy season,” he said.

In every outbreak, the Ministry of Public Health investigates and often blames contaminated drinking water. However, in reality, testing is usually conducted at late stages, by which time the virus has spread widely and drinking water is blamed because of the high viral load. 

“The exact initial cause of an outbreak is often unknown, but based on available information, we believe the source is likely migrant workers who brought the virus into the country and spread it in clusters within factories.

“However, this is very difficult to detect. It’s not surprising that outbreaks occur in factories with a large number of people. It’s crucial that food factories and restaurant personnel maintain high hygiene standards, especially washing hands thoroughly after using the restroom. Vaccination of these personnel, if possible, is essential to reduce outbreaks,” he said.

Another significant source of transmission is seafood. The virus is highly resilient in seawater, and many shellfish, when consuming plankton or other food sources, ingest the virus. If the food is not cooked thoroughly enough, the virus will not die. Generally, temperatures above 85 degrees Celsius are needed to kill the virus. Therefore, consuming thoroughly cooked food (over 100 degrees Celsius) is safe. 

However, eating raw shellfish like cockles or oysters, where the internal temperature isn’t high enough, could be a source of transmission, similar to the Shanghai outbreak 30-40 years ago which infected hundreds of thousands of people.

While improved hygiene and the use of individual bottles of drinking water have led to fewer outbreaks of Hepatitis A, with only minor cases reported recently, Dr. Yong pointed out over 20 years, there were several major outbreaks. 

“The largest I witnessed was the Chiang Rai outbreak in 2005, which affected a large number of people. Two people died from the disease. A major outbreak occurred again in 2012 in Bueng Kan province. 

“We studied Hepatitis A immunity in the Thai population, as shown in the chart. It can be seen that currently, the majority of the Thai population, especially those under 40 years old, do not have natural immunity to Hepatitis A. Immunity to Hepatitis A gradually increases after the age of 40, and those over 60 years old have almost 100 percent immunity, as shown in the chart,” he said.

The most prominent symptom of Hepatitis A is jaundice (yellowing of the skin and eyes). Patients will have a fever on the first day, but the fever is usually not high. They may also experience nausea, vomiting, abdominal pain, and in some cases, diarrhoea. These symptoms usually only last for the first few days, after which yellowing of the skin and eyes begins. The mortality rate is relatively low. Most deaths occur in individuals over 40 years old who have pre-existing liver disease or have weakened immune systems due to underlying conditions.

Hepatitis A can be prevented with a vaccine, but currently, this is quite expensive and not yet mandatory. Therefore, vaccination is self-funded. Since a large portion of the population lacks immunity, the entry and spread of Hepatitis A virus in the population could lead to an outbreak.

CAPTIONS:

Top – Dr. Yong Poovorawan and a patient suffering from Hepatitis A infection. Photo – PPTVHD36

Insert – A chart showing Hepatitis A infection in Thailand.  Shared by  Dr. Yong Poovorawan and published by PPTVHD36

Front Page – A diagram of Hepatitis A infection. Credit Southgate Medical