Fast Facts
What is influenza?
Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses.
Fast Facts
How common is influenza?
Influenza is one of the most common infectious diseases, with around one billion cases globally each year.
Fast Facts
Can influenza be treated?
Influenza can be treated with prescription antiviral medications, but vaccination is the most effective way to prevent unpleasant or severe symptoms.
Influenza, commonly called the flu, is a respiratory virus infection that impacts the nose, throat, lungs and, in some cases, the intestinal tract. The flu easily spreads through coughs or sneezes. Most individuals with the flu recover without the need for medical intervention, but in some cases, the infection can be severe or even fatal.
An annual flu shot is recommended to help reduce the risk of contracting the seasonal flu. While the vaccine does not offer complete protection, it significantly decreases the likelihood of severe complications and the requirement for hospitalization, particularly for those at high risk.
Influenza basics
1 billion cases There are approximately one billion cases of seasonal flu annually, including three to five million cases of severe illness.
1-4 days Symptoms begin one to four days after infection and usually last for a week.
99% In developing countries, flu-related lower respiratory infections cause 99% of deaths in children under five.
650,000 deaths each year Approximately 290,000 to 650,000 people are killed by the flu annually.
There are four kinds of influenza viruses, each the sole member of its own genus: types A, B, C and D. Influenza A and B viruses are responsible for the seasonal epidemics of disease during flu season.
Influenza A
Influenza A viruses can infect people and animals, often resulting in more severe symptoms and a higher number of cases. Birds are the primary reservoir of influenza A, but the viruses also circulate among mammals. An influenza A virus is responsible for the 1918 Spanish flu pandemic.
Influenza B
Influenza B viruses mostly cause disease in people, though they can also do so in some animals like seals and pigs. These infections are often milder than those caused by influenza A viruses but still pose a danger to young children.
Influenza C
According to the World Health Organization, influenza C viruses are detected less often and typically result in mild infections. They are not considered a public health concern.
Influenza D
Influenza D viruses primarily affect cattle and pigs. They can infect humans, causing mild or subclinical illnesses.
These influenza viruses differ from the viruses responsible for the stomach flu, which cause diarrhea and vomiting.
Influenza A and B viruses infect all ages but mainly cause severe illness in people over 65, young children and those with chronic conditions.
The flu can progress into pneumonia, triggered either by the virus itself or a secondary bacterial infection. Additional complications include acute respiratory distress syndrome, meningitis, encephalitis and the worsening of pre-existing conditions, like asthma and heart disease.
Influenza in Florida
Flu seasons vary in timing, severity and duration. It’s impossible to predict what each flu season will be like in Florida. The Florida flu-reporting year follows the standard 52- or 53-week-per-year reporting schedule outlined by the Centers for Disease Control and Prevention. Although flu season ends in May, or week 20, surveillance continues year-round. Cases historically increase in October as holiday-related travel increases.
Individual cases are not reportable to the Florida Department of Health, except for new subtypes of influenza A and flu-associated pediatric deaths. All outbreaks are reportable in Florida.
Influenza transmission
Aerosols are the primary mode of transmission of influenza viruses. These are emitted when people exhale, speak, sing, cough, sneeze or blow their nose. Virus particles can remain in the air for extended periods.
People can also transmit influenza to their pets in a process called reverse zoonosis.
Symptoms of influenza
Common flu symptoms include body aches, fever and chills. While a common cold shares these symptoms, it will generally have a slower onset than the flu. Flu symptoms appear two or three days after viral exposure. In addition, flu symptoms tend to be more severe than those of the common cold.
Other common flu symptoms include:
- Sore throat
- Runny nose
- Cough
- Headache
- Fatigue
- Sweating
In children, flu symptoms may manifest more generally as fussiness or irritability. Children with the flu are also more likely than adults to experience ear pain, nausea or vomiting. In some cases, people experience eye pain, watery eyes or light sensitivity.
Populations most vulnerable to influenza infections
Anyone can get the flu, but infections can be more severe in children younger than two, those over 65, pregnant people and those with underlying health conditions.
It is possible to experience flu alongside other respiratory illnesses, including COVID-19. Researchers are still determining the frequency of this occurrence, so vulnerable groups need to remain vigilant to prevent coinfection.
Influenza diagnosis
Several tests can detect flu viruses, the most common being rapid influenza diagnostic tests. RIDTs can detect virus antigens and give results in five to 15 minutes. Other tests, known as rapid molecular assays, detect virus genetic material, with results available in 15 to 30 minutes.
More accurate flu tests can be performed in specialized labs such as hospitals and public health facilities. These tests require a healthcare provider to swab the nose or throat and send the sample for testing. Results can take hours to become available.
During a flu outbreak, a positive rapid flu test usually indicates a flu infection. However, the accuracy of rapid tests can differ based on the type of test used and the circulating flu viruses. This variability can lead to some infected individuals receiving a false negative rapid test result. A health care provider might still decide on a flu diagnosis based on symptoms and their clinical judgment if a rapid test comes back negative. Rapid tests tend to be more effective at detecting the flu in children than in adults.
Influenza treatment
Because the flu is caused by a virus, antibiotics are ineffective. Antiviral drugs may be a treatment option, but mainly in severe cases. Influenza antiviral drugs are prescription medicines like pills, liquids, inhaled powders or intravenous solutions that fight against flu in the respiratory tract.
Most people with flu experience a mild illness and do not need medical care or antiviral drugs. If you develop flu symptoms, you should only be in contact with other people if you seek medical care. Early treatment is advised for high-risk individuals with flu or suspected flu, especially those with conditions like asthma, diabetes or heart disease.
Influenza prevention
The vaccine is the most effective way to prevent the flu. There are yearly rounds of vaccines for whichever flu strain is currently circulating. The body needs about two to four weeks following the vaccine to build immunity. It is recommended to receive the shot before the start of flu season to ensure immunity is established during the peak transmission period.
In addition to vaccination, take other preventive measures to reduce the spread. Avoid close contact with sick individuals. If you are ill, limit your interactions to prevent spreading the virus to others. For flu, the CDC advises staying home for at least 24 hours after your symptoms improve and you no longer have a fever without using fever-reducing medication. To avoid getting sick, remember to do the following:
- Disinfect surfaces.
- Cover your mouth when coughing or sneezing.
- Discard tissues after use.
- Wear a mask to help prevent virus spread and protect others.
- Wash your hands often, use alcohol-based sanitizer and avoid touching your face.
- Improve air quality by ventilating or gathering outdoors to reduce the risk of exposure.
Additional resources
Article
How to avoid winter viruses: UF EPI expert talks RSV, flu and COVID-19
With winter comes a trio of respiratory illnesses, sometimes referred to as a “triple-demic”: influenza, COVID-19 and respiratory syncytial virus, or RSV. Learn how to avoid viruses during the cold, dry weather.
Student resource
Flu Vaccinations at the Student Health Care Center
We all can play a role in caring for ourselves and our community, whether that’s by getting vaccinated or wearing a mask. We can also do our part by getting vaccinated for influenza, which can prevent you from getting sick and from spreading the flu virus to others.
Student Resource
FLU: What to Do if You Get Sick
The UF Student Health Care Center answers frequently asked questions regarding influenza, courtesy of the Centers for Disease Control and Prevention. These answers include how to react if you get sick, which medications to take and how long one should wait until returning to work or classes.
Hospital Resource
Influenza
The flu is a viral respiratory illness that causes fever, chills, runny nose, body aches and cough. It spreads easily from person to person. The flu can cause moderate to severe symptoms. Most people recover fully. Children, older adults and people with certain health conditions are at risk for severe illness and even death.