Gaby
There’s an old joke: if you treat a cold or the flu, it lasts a week; if you don’t, it lasts seven days. How accurate is that folk wisdom, and what else don’t we really know about this well-studied illness?
A Familiar Stranger
The flu is an acute respiratory viral infection that humans have known about for thousands of years. Hippocrates recorded an outbreak of a “Perinthian cough” as early as 412 B.C., describing a respiratory illness with flu-like symptoms. A similar disease, called “peasant fever,” struck England in 1173. Large flu outbreaks have been documented since the 1500s; in Europe alone, three epidemics occurred in the 18th century. One of them, from 1781 to 1782, is considered the largest in history, infecting more than three-quarters of England’s population.
Flu viruses were only isolated in the 20th century (influenza A in birds in 1901, influenza A in pigs in 1931, and influenza A, B, and C in humans in 1933, 1940, and 1951), but the name influenza—Italian for “influence”—entered European languages in the mid-18th century. One idea is that the term reflected how the disease could strongly affect public health.
Another theory links the name to Renaissance-era astrology, where disease was blamed on unfavorable celestial influences. The English shorthand “flu” (French la grippe; German die Grippe) may come from a word meaning “to catch.” In some Slavic languages, the word for flu resembles the word for “wheeze,” which ties to the illness’s symptoms.
Although specific viruses cause the flu (more than 2,000 variants are known today), similar symptoms can appear in many other acute respiratory viral infections (ARVI). Because of that overlap, doctors call some illnesses “flu-like.” More than 200 types of respiratory viruses—rhinoviruses, adenoviruses, respiratory syncytial viruses, and others—can produce similar conditions. So it’s incorrect to label every ARVI as “the flu.”
Flu Pathogens
Flu viruses fall into three main types that differ in how they spread and how severe the illness can be. Influenza A is the most common cause of seasonal flu and is considered the most dangerous because it infects both humans and animals and can jump between species—people, livestock, and birds. Influenza A causes moderate to severe illness and is the only type known to trigger pandemics.
Influenza B causes more localized outbreaks and affects only humans, primarily children. Influenza A epidemics tend to occur every 2 to 3 years, while influenza B outbreaks show up roughly every 4 to 6 years; B infections can precede or occur alongside A. Influenza C also infects humans—mainly children and immunocompromised adults—but it usually causes mild or no symptoms and does not drive epidemics or major complications.
The flu spreads easily via respiratory droplets when people cough, sneeze, or talk. Infection often leads to lasting immunity in the individual, but people with weakened immune systems are much more likely to contract the virus. All age groups are susceptible, but the highest risk is for those 65 and older, followed by people aged 50 to 64. Children, pregnant people, and people with chronic heart or lung disease are also at higher risk of severe illness.
Seasonal Nature
Flu peaks around thawing weather: at temperatures near 0°C the virus can survive longer—sometimes up to a month. The highest risk of infection is between about -5°C and +5°C. Cold, dry air makes airways more vulnerable, which helps the virus gain a foothold when humidity drops. Yearly and seasonal outbreaks (usually in fall and winter) happen because the virus constantly changes its antigens through drift and shift. Frequent antigenic changes while the virus circulates in nature help explain why new strains with stronger symptoms appear each year.
The flu mainly attacks the upper respiratory tract and the bronchi and less often the lungs. It stands out among viral infections for its potential to become severe and cause high mortality during seasonal epidemics, which affect roughly 8% to 15% of the population. Each year up to 500 million people worldwide may be infected, and as many as 2 million can die. In terms of deaths, flu ranks around eighth among all diseases (between diabetes and kidney disease), so it shouldn’t be taken lightly.
Most people who catch the flu don’t see a doctor. An analysis of data from 2005 to 2011 published in The Lancet Respiratory Medicine found that only about one-fifth of infected people showed symptoms, and only 17% of those consulted a physician. Meanwhile, people with the virus spread it during their illness: through aerosols, an infected person—even with mild symptoms—can be contagious from the first hour up to the fifth to seventh day of illness. That’s why isolating sick people during flu season, wearing masks, and avoiding crowded places are important. Because the virus mutates constantly, medicine still lacks foolproof antivirals, and achieving herd immunity by vaccination would require about 80% of healthy people and 90% of at-risk groups to be immunized.
Flu Symptoms
The flu can infect the upper and lower respiratory tracts, with symptoms appearing 1 to 4 days after exposure. Early diagnosis is tricky because initial symptoms resemble other respiratory infections. Because many ARVI look alike, confirming the flu requires laboratory tests: the virus can be identified from epithelial cells of the nasal mucosa, throat swabs, or blood tests. Nonspecific lab studies include blood and urine analysis. A chest X-ray is often used during examination to detect complications.
When tests aren’t available, clinicians diagnose the flu based on local epidemiology—whether others in the area are sick at the same time. The flu typically appears suddenly, with an incubation period ranging from 3–24 hours up to 2–5 days after infection (on average about 1–2 days).
The main signs of the flu include:
- high body temperature—fever (antipyretics may not lower it for a week);
- marked weakness;
- muscle and joint aches;
- severe headache;
- nasal congestion;
- dryness in the nose and throat;
- throat and tracheal pain (chest discomfort);
- persistent cough;
- excessive sweating;
- tearing;
- sensitivity to light and sound;
- skin rashes;
- loss of appetite.
Other possible signs include reduced nasal sensation, dizziness, dry mouth, a glazed look in the eyes, ringing in the ears, coating on the tongue and lips, cracks at the corners of the mouth, rapid breathing, a high pulse, and irritability. The patient’s condition may improve or worsen in waves.
How Long Does the Flu Last?
Depending on how severe the infection is, overall health, age, and prior exposure to similar strains, the flu can run a mild, moderate, or toxic course. In mild cases, the fever may be absent or only slightly elevated (around 38°C). Moderate cases produce temperatures of 38.5–39.5°C. In severe toxic forms, body temperature can reach 40°C, and the patient may suffer seizures, vomiting, nosebleeds, and hallucinations.
Stomach pain and diarrhea are not core symptoms of the respiratory flu, though they occur often with other viruses. For example, gastroenteritis is most commonly caused by rotavirus, which inflames the gastrointestinal tract. “Stomach flu” should not be confused with influenza: rotavirus infection is treated differently, and its typical signs include severe vomiting and dehydration.
There are some distinctions between the flu and other viral respiratory infections. With the flu, fever tends to spike quickly to a high level; with a common cold, fever is usually below 38°C and less common. Colds often cause more sneezing and nasal discharge, while the flu more often produces a blocked feeling in the nose. In many other ARVI, sneezing is common but eyes rarely tear or redden and cough may be absent—whereas a flu cough can last more than two weeks.
A person with the flu is most contagious around the third to fourth day after symptoms begin. If there are no complications, fever may last 2–4 days and recovery usually occurs within 7–10 days. Most people recover within a week without medical care, but severe cases can take up to 15 days to treat. Weakness, irritability, sleep problems, and headaches can linger for two to three weeks after recovery.
Treatment of the Flu
Avoid lowering a fever below 38°C with medication—fever helps the body’s defenses fight the virus. Don’t treat the flu without consulting a doctor, because improper self-treatment can lead to complications.
Doctors commonly recommend:
- antihistamine tablets;
- nasal sprays and drops to relieve congestion;
- isotonic saline for nasal rinsing and short-term vasoconstrictor drops;
- medications for throat irritation and pain;
- cough suppressants and expectorants to thin mucus.
Until the 1960s, people relied only on symptom relief. Today treatment still centers on symptomatic care—disinfectants, hemostatics, and analgesics—combined with targeted measures when needed.
Keep fluids up and aim to drink about 2 liters of water a day during illness. Helpful drinks include rosehip infusion, fruit drinks, lemon tea, and other warming beverages rich in vitamin C. Fluids help flush out toxins released by the virus.
Home remedies that can provide comfort include:
- gargling herbal infusions—chamomile, eucalyptus, sage, coltsfoot;
- aromatherapy with essential oils like lavender, eucalyptus, peppermint, rosemary, chamomile, and lemon;
- alkaline-oil inhalations.
Antiviral medications are most effective if started early, before severe clinical manifestations develop; delayed use is less effective. Antibiotics do not treat viral flu; they’re only justified if a bacterial inflammatory or purulent complication develops, such as pneumonia, bronchitis, otitis, or sinusitis.
Beyond bacterial complications, the flu can provoke problems in the cardiovascular or nervous systems (meningitis, encephalitis, and similar conditions). To recover fully, bed rest is crucial. Avoid getting up, using a computer, reading, or watching TV—these activities add strain and can prolong recovery.
Call a doctor if you notice:
- loss of consciousness;
- breathing difficulties (shortness of breath), especially in children—difficulty breathing except when leaning forward is critical;
- sharp side rib pain when coughing;
- coughing up pink or bloody mucus;
- high fever that does not drop after three consecutive doses of different antipyretics (allowing for each drug’s onset time);
- fever that falls to 37–37.5°C and then rises again to 38°C or higher, which may signal a secondary infection.
Fatal outcomes from the flu are most likely in infants under 2 years old and in people 65 and older. In those cases, call emergency services without hesitation.
Flu Prevention
To reduce risk before the seasonal surge, vaccination and, in some cases, antiviral medications are sensible options. To minimize the chance of a seasonal flu, get vaccinated in October—this gives the body time to build protective immunity before cold weather arrives. Interferon and immunoglobulin may be used for emergency prevention when indicated.
Antiviral drugs can protect unvaccinated people in closed settings or during an epidemic and may be recommended for at-risk individuals. Antivirals reduce symptoms and shorten illness duration when taken as prescribed by a doctor. In some preventive regimens the course can last 1–2 months.
Prevent the virus from reaching mucous membranes: ventilate rooms regularly, humidify indoor air, take warm baths, and rinse the nose with saline. The flu virus isn’t harmed by frost, but it is vulnerable to regular soap, drying, and temperatures above 70°C.
Reduce contact with sources of infection, get fresh air, maintain hygiene, and support your immune system. Quitting harmful habits, avoiding excessive stress, getting enough sleep, eating a balanced diet, and staying active are as important in fighting the flu as disinfection and clean hands.
