Hepatitis, malaria, and legionellosis: which diseases return from vacation with tourists

      The increase in visits to infectious disease specialists at the end of August and September follows a clear pattern: people return from vacations, and for several weeks, doctors observe a surge in the same diagnoses. The difficulty lies in the fact that not all patients inform their doctors about their travels, which can delay accurate diagnosis for a dangerous period.

      Change of environment as a risk factor

      According to infectious disease specialist Andrei Pozdnyakov from Invitro, the risk of contracting an infection while traveling increases not due to "weakened immunity" in the everyday sense, but because of exposure to a new microbial environment. In their region, a person lives in balance with the local microflora, having partial immunity to it. However, while traveling, they encounter different serotypes of bacteria, viruses, and parasites that their body is not prepared for.

      Moreover, during vacations, familiar hygiene barriers cease to function: ice in drinks, street food, swimming with water ingestion, shared pools, and buffets with dishes at room temperature—all of these become transmission routes for infections that a person usually avoids in everyday life. Crowding also plays a role: airports, airplanes, buses, and tour groups create conditions for the spread of respiratory infections.

      Experts also point out the decrease in adaptive reserves: changes in climate and time zones, lack of sleep, alcohol, prolonged sun exposure—these factors genuinely increase the likelihood that an encounter with a pathogen will result in illness.

      The main trap: the incubation period

      A key point emphasized by the infectious disease specialist concerns the timing of symptom manifestation. The incubation period for different infections varies from a few hours to many months. The practical consequence of this is that a person almost never falls ill in the place where they were infected. A tourist returns home healthy, goes to work, and after a week, two, or a month, encounters a fever. By this time, the trip is already forgotten, and the doctor may begin treating the patient for "ordinary ARVI" or "poisoning," missing the critical time.

      What diagnoses do doctors see most often

      The most common group is intestinal infections and the so-called "traveler's diarrhea." Pathogens include enterotoxigenic Escherichia coli, Campylobacter, Salmonella, Shigella, norovirus, and rotavirus. The transmission route is fecal-oral. The incubation period is short, so such infections usually start during the trip or in the first days after returning: for viral infections—12–48 hours, for bacterial infections—up to three days. However, protozoan infections, such as giardiasis and amoebiasis, may manifest after several weeks or months, and they are often confused with irritable bowel syndrome.

      The classic "vacation" infection remains hepatitis A. Its incubation period ranges from 15 to 50 days, averaging about a month. Thus, a person who vacationed in July may fall ill at the end of August. The first symptoms are nonspecific: weakness, nausea, aches, fever—similar to ARVI. Jaundice, if it appears, occurs later, and the connection to the trip is no longer obvious by that time.

      Among respiratory infections, the most common findings are ARVI, influenza, and COVID-19, with infections occurring most frequently at airports and on airplanes. Their incubation period is short—from one to seven days. The doctor also mentions legionellosis, which is rarely considered: the pathogen multiplies in air conditioning systems, plumbing, and hotel showers, and infection occurs through inhalation of water aerosol. It manifests as severe pneumonia 2–10 days after contact.

      Measles, which has seen an increase in incidence in recent years, is also often imported from abroad. It is one of the most contagious infections: a susceptible unvaccinated person is almost guaranteed to become infected when in the same room as an infected individual. The incubation period is from 7 to 21 days, with the disease starting with fever, runny nose, cough, and conjunctivitis, while the rash appears later. In the first days, the patient is already contagious and can transmit the virus to others. Adults, as the specialist notes, experience measles more severely than children.

      Particular attention—tropical infections

      The most concerning group in recent seasons, according to the doctor, is infections transmitted by mosquitoes. According to Rospotrebnadzor, only in the first five months of 2026, Russia imported 127 cases of dengue fever—compared to 178 cases for the entire year of 2025. In total, around 40 different infections were imported into the country last year, including malaria, chikungunya, West Nile fever, cholera, and Zika.

      Dengue fever manifests 3–14 days after a bite (most often on days 4–7): high fever, severe headache, and muscle-joint pain, along with a rash. The danger is that a second infection with a different serotype is more severe. Chikungunya presents itself 1–12 days later and is characterized by debilitating joint pain, which can persist for months in some patients.

      However, the main threat, according to the expert, is malaria. Its incubation period starts from seven days, and for some species of the pathogen, it can extend for many months or even over a year. Tropical malaria can lead to life-threatening conditions in just a few days. Therefore, the rule is categorical: any fever after returning from the tropics—Africa, Southeast Asia, Latin America—requires immediate medical attention and exclusion of malaria as a priority.

      What is important to remember after vacation

      The expert provides several practical recommendations. First, for any malaise within two months after the trip, it is essential to inform the doctor where you were and when you returned. This information changes the direction of diagnostic searching.

      Second, do not start taking antibiotics on your own. They are useless for viral infections, not always necessary for intestinal infections, and most importantly, they obscure the clinical picture and make examinations less informative.

      Third, there is a list of symptoms for which you should seek medical attention immediately: a temperature above 38 degrees after returning from the tropics, jaundice of the skin or sclera, dark urine, diarrhea lasting more than three days or with blood, pronounced shortness of breath, rash against a background of fever, as well as any recurrent fever after seeming recovery.

      Fourth, examinations in the absence of symptoms but with risky situations (questionable food and water, swimming in stagnant water, mosquito bites in endemic regions, unprotected contacts) should not be planned immediately but should take into account the incubation period of the specific infection. Too early testing may provide false reassurance.

      The main conclusion drawn by the specialist is that vacation does not end on the day of return but approximately a month later. During this entire time, it is advisable to pay more attention to one's well-being than usual and not hesitate to mention the trip during a doctor's appointment.