Influenza Health Article

Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease caused by certain strains of influenza virus. When the virus is inhaled it attacks cells in the upper respiratory tract causing typical flu symptoms such as fatigue, fever and chills, hacking cough, and body aches. Influenza victims are also susceptible to potentially life-threatening secondary infections. Although the stomach or intestinal upsets and diarrhea are commonly called "flu," the influenza virus rarely causes gastrointestinal symptoms. Such symptoms are most likely due to other organisms such as rotavirus, Salmonella, Shigella, or Escherichia coli.

Description

Influenza is considerably more debilitating than the common cold. Influenza outbreaks occur suddenly and infection rapidly spreads. The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone.

Influenza outbreaks occur on a regular basis. Pandemics, the most serious outbreaks, affect millions of people worldwide and last for several months. The 1918–1919 influenza outbreak serves as the primary example of an influenza pandemic. In that Spanish flu pandemic, the death toll reached a staggering 20–40 million people worldwide. Approximately 500,000 of these fatalities occurred in the United States. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu was responsible for 70,000 deaths in the United States, while the Hong Kong flu killed 34,000 people.

Epidemics are widespread regional outbreaks that occur every two to three years and affect 5–10% of the population. The Russian flu in the winter of 1977 is an example of an epidemic. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

The earliest existing descriptions of influenza were written nearly 2,500 years ago by the ancient Greek physician, Hippocrates. Historically, influenza was ascribed to a number of different agents, including "bad air" and several different bacteria. It was not until 1933 that the causative agent was identified as a virus.

There are three types of influenza viruses, identified as A, B, and C. Influenza A can infect a range of species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C viruses are less common and cause a milder illness.

Causes and symptoms

Approximately one to four days after infection with the influenza virus, a person is hit with an array of symptoms. "Hit" is an appropriate term, because symptoms are sudden, harsh, and followed by overall bodily aches and a fever that may run as high as 104°F (40°C). As the fever subsides, nasal congestion and a sore throat become noticeable. Persons with the flu feel extremely tired and generally miserable. Typical influenza symptoms include the abrupt onset of a headache, dry cough, and chills, and a rapid onset of physical weakness. Normal energy levels typically do not return for several days, but this can extend up to two weeks.

Influenza complications usually arise from secondary bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as a person seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough with thick, yellowish-green sputum. If these symptoms appear, medical treatment is necessary. Other secondary infections, such as sinus or ear infections, may also require medical intervention. Heart and lung problems and other chronic diseases can be aggravated by influenza. This is a particular concern among elderly people.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome, a rare but serious complication of the flu. Symptoms of Reye's syndrome are nausea and vomiting, and—more seriously— neurological problems such as confusion or delirium. Among children Reye's syndrome can be fatal. The syndrome has been associated with the use of aspirin to relieve flu symptoms.

Diagnosis

Although specific laboratory tests can be performed on respiratory samples to identify a flu virus strain, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little to influence individual treatment. Doctors may administer tests, such as throat cultures, to identify and treat secondary bacterial infections.