Gastrointestinal diseases represent one of the main reasons for medical consultations worldwide. According to the World Health Organization (WHO), digestive tract infections affect millions of people every year, and are especially dangerous for children under five and older adults. In a world where globalization accelerates the movement of people and food, pathogens that affect the stomach and intestines find fertile soil to spread. Knowing which viruses and germs are most common, how they are transmitted, and how to prevent them is, now more than ever, an essential tool for public health. Viruses that most commonly affect your stomach: Every year, millions of people worldwide experience the characteristic symptoms of a gastrointestinal infection: nausea, vomiting, diarrhea, fever, and abdominal pain. Although many attribute these episodes to simple "food poisoning," behind these infections lies a universe of microorganisms—viruses, bacteria, and parasites—that attack the digestive system with different strategies and levels of aggressiveness. Which are the most frequent? How do they enter the body? Is it possible to avoid them?

Norovirus: the champion of contagion. If there's one virus that deserves the title of "king of the upset stomach," it's norovirus. Responsible for approximately 20% of all cases of acute gastroenteritis worldwide, this pathogen is extremely contagious: ingesting just 18 viral particles is enough to infect a person. It is transmitted through contaminated food and water, infected surfaces, and contact with sick people. Symptoms appear between 12 and 48 hours after exposure and usually include severe vomiting, diarrhea, abdominal cramps, and sometimes a low-grade fever. While the illness generally resolves on its own in one or two days, it can be dangerous for older adults and people with compromised immune systems. There is no specific antiviral treatment, and the virus is notoriously resistant to many common disinfectants. Which makes it the culprit behind massive outbreaks on cruise ships, in nursing homes, and in schools.

Rotavirus: the enemy of the little ones. Before the advent of vaccines,Rotavirus was the leading cause of severe diarrhea and death in children in developing countries. This virus most severely affects children under five, causing episodes of profuse watery diarrhea, vomiting, and fever that can lead to severe dehydration in a matter of hours. It is mainly transmitted via the fecal-oral route, that is, through dirty hands, contaminated surfaces, or improperly handled food. The good news is that effective vaccines now exist that have drastically reduced their impact in countries where they have been implemented in childhood immunization schedules. However, it remains an active threat in regions with limited access to clean water and inadequate sanitation systems.

Enteric adenovirus: the silent intruder.

Less well-known than the previous ones, enteric adenovirus—especially serotypes 40 and 41—is a common cause of gastroenteritis in children and immunocompromised adults. Unlike norovirus, which acts quickly and brutally, enteric adenovirus takes its time: the incubation period can last up to 10 days, and symptoms—prolonged diarrhea, vomiting, and moderate fever—can persist for more than a week. It is spread through direct contact with infected people or contaminated surfaces. There is no vaccine available to the general public, and treatment is limited to managing symptoms and preventing dehydration. Salmonella: When bacteria disguise themselves as viruses. Although technically not a virus but a bacterium, Salmonella deserves a prominent place on this list as one of the most common causes of foodborne illness worldwide. It is primarily found in raw or undercooked eggs, poultry, unpasteurized dairy products, and contaminated fruits and vegetables. Symptoms—diarrhea, high fever, cramps, and vomiting—usually appear between 6 and 72 hours after ingesting contaminated food and can last up to a week. In most cases, it resolves without antibiotic treatment, although in vulnerable individuals it can spread to the bloodstream and become a medical emergency. Campylobacter: the most common one that no one mentions. Despite being the most frequent cause of bacterial diarrhea globally, Campylobacter remains the great unknown of dangerous gastronomy. Its main source of transmission is undercooked chicken and untreated water. Symptoms include severe diarrhea—sometimes with blood—fever, nausea, and severe abdominal pain, and usually appear between two and five days after exposure. In rare but serious cases, the infection can lead to Guillain-Barre syndrome, a serious neurological disorder. The key to preventing it lies in thoroughly cooking food and maintaining strict hygiene during preparation.

Escherichia coli (E. coli): When an everyday bacterium becomes dangerous. It is a bacterium that naturally inhabits the intestines of humans and animals, and in most cases it is completely harmless. However, certain strains—particularly O157:H7,which produces potent toxins—can trigger severe digestive problems. Its main route of transmission is the consumption of undercooked ground beef, unpasteurized milk, leafy green vegetables contaminated with animal feces, and untreated water. Symptoms appear three to four days after exposure and include severe diarrhea—often bloody—abdominal cramps, and vomiting. In most healthy adults, the infection clears up within a week. But in young children and older adults, the O157:H7 strain can cause hemolytic uremic syndrome (HUS), a serious complication that affects the kidneys and can be fatal. A counterintuitive detail that surprises many: in infections caused by toxin-producing strains, the use of antibiotics is not recommended, as it can increase the risk of developing HUS by releasing more toxins into the bloodstream. Listeria monocytogenes: the silent threat of refrigerated foods. It has a characteristic that distinguishes it from almost all other digestive pathogens: it can grow and multiply at refrigeration temperatures, making it a hidden danger in foods we consider safe because they are cold. Deli meats, soft cheeses made with unpasteurized milk, smoked salmon, pates, and ready-to-eat salads are its main reservoirs. In healthy people, the infection may go unnoticed or manifest as a mild fever with gastrointestinal discomfort. The real danger lies in vulnerable populations: pregnant women, the elderly, newborns, and immunocompromised individuals. In these groups, listeriosis can spread beyond the intestine, reaching the central nervous system and causing meningitis, septicemia, or, in the case of pregnant women, miscarriage, premature birth, or severe infection in the newborn. The mortality rate in invasive cases can exceed 20%, making it one of the deadliest foodborne illnesses. Prevention involves avoiding high-risk foods during pregnancy or in situations of immunosuppression, respecting expiration dates, keeping the refrigerator below 4°C, and regularly cleaning its internal surfaces. Giardia lamblia: the waterborne parasite. It is a microscopic parasite found in contaminated water sources.Soils and surfaces that have come into contact with feces from infected animals or humans. Unlike viruses, which cause acute and brief symptoms, giardiasis can become a chronic infection if left untreated: persistent, oily diarrhea, excessive flatulence, abdominal distension, and weight loss are its hallmarks. It is especially common in travelers visiting regions with poor sanitation—hence the popular term “traveler's diarrhea”—and in children attending daycare. Diagnosis requires stool analysis, and treatment is with specific antiparasitic drugs.

How to protect yourself: the keys to prevention

Given this situation, public health experts agree that prevention remains the most effective weapon. Washing your hands with soap and water for at least 20 seconds—especially before handling food and after using the toilet—,Cooking food to appropriate temperatures, avoiding drinking water from unverified sources, and keeping kitchen surfaces clean are simple measures that make a substantial difference. In addition, timely hydration is essential once symptoms appear: oral rehydration solutions can prevent serious complications, especially in children and older adults. And when symptoms are severe or prolonged, medical consultation should not be delayed. The stomach is, to some extent, a window into our relationship with the environment. Being mindful of what we eat, how we prepare it, and who we share our space with is also a way of taking care of ourselves.