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In 2017 Chile experienced a significant hepatitis A outbreak. During the first half of that year the number of cases surged, and in some regions the incidence rose to more than ten times the figure recorded in the same period the year before. Unlike the classic pattern of hepatitis A, tied to water and food, in that outbreak sexual transmission, especially among men who have sex with men, played a central role.

This article is kept as reference and background material. It does not describe a current alert, but an event that has already passed and left lessons that remain useful today: why hepatitis A can be more serious in adults, why Chile now has a growing number of susceptible people, and why the vaccine is the best prevention tool in at-risk groups.

What happened in 2017?

Chile’s 2017 outbreak was not an isolated event. It coincided with similar outbreaks described in several countries. In the European Union, between June 2016 and May 2017 more than 4,000 cases were reported linked to a multi-country outbreak in which the great majority of those affected were men who have sex with men, many of them unvaccinated. That pattern, sexual transmission among adults rather than childhood spread through water or food, was the same one seen in Chile.

Hepatitis A is transmitted by the fecal-oral route. In sexual practices, particularly those involving oral-anal contact, the virus passes easily from one person to another. That is why, in adult populations with many contacts and low prior immunity, the virus can circulate quickly.

Why are more adults now susceptible in Chile?

For decades Chile was a country with high hepatitis A endemicity: almost all children were infected at an early age, usually mildly, and remained protected for life. As drinking water, sanitation and living conditions improved, that early exposure fell sharply. Chile became a country of intermediate endemicity.

The result is a paradox: with fewer infections in childhood, there are more adolescents and adults who were never infected and therefore have no defenses. This growing pool of susceptible people is what allows outbreaks like the one in 2017 to occur once the virus starts circulating.

Why is it more concerning in adults?

Hepatitis A almost always resolves on its own and does not become chronic, but its severity depends heavily on age. In children it usually goes almost unnoticed. In adults, by contrast, it tends to cause more symptoms, more pronounced jaundice and a slower recovery. A proportion of adults require hospitalization, and although acute liver failure is rare, it is more likely in this group.

The risk is even higher in two situations:

  • People with pre-existing liver disease, such as those with advanced fatty liver disease, chronic hepatitis B or hepatitis C, or cirrhosis. In them, hepatitis A can decompensate an already damaged liver.
  • HIV coinfection or other conditions that affect immunity.

In recent person-to-person outbreaks, a high proportion of affected adults ended up hospitalized, confirming that in this population the disease is far from trivial.

How is it prevented?

The most effective measure is the hepatitis A vaccine, which is very safe and provides long-lasting protection. In a country of intermediate endemicity like Chile, international recommendations point to vaccinating the groups at greatest risk of infection or severe disease. Among them:

  • Men who have sex with men.
  • People with chronic liver disease of any cause.
  • People with HIV.
  • Travelers to areas where the virus circulates widely.
  • People who use drugs.

To this are added the general measures that reduce transmission: careful hand washing, food hygiene and, in the sexual context, safer practices. If you had a recent high-risk contact, the vaccine given early also works as prophylaxis after exposure; consult your doctor promptly.

If you belong to one of the at-risk groups and do not know whether you are protected, talk to your doctor. A blood test can show whether you already have defenses (IgG antibodies against the virus), and if you do not, vaccination is the safest way to avoid the disease.

See also

References

  1. Ndumbi P, et al. Hepatitis A outbreak disproportionately affecting men who have sex with men (MSM) in the European Union and European Economic Area, June 2016 to May 2017. Euro Surveill. 2018;23(33):1700641.
  2. Nelson NP, et al. Prevention of Hepatitis A Virus Infection in the United States: Recommendations of the Advisory Committee on Immunization Practices, 2020. MMWR Recomm Rep. 2020;69(5):1-38.
  3. Foster MA, et al. Widespread Hepatitis A Outbreaks Associated with Person-to-Person Transmission - United States, 2016-2020. MMWR Morb Mortal Wkly Rep. 2022;71(39):1229-1234.
  4. Van Damme P, et al. Hepatitis A virus infection. Nat Rev Dis Primers. 2023;9(1):51.
  5. WHO position paper on hepatitis A vaccines: June 2012-recommendations. Vaccine. 2013;31(2):285-286.
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