Influenza

What is Influenza?

Influenza is an acute infectious disease caused by one of the influenza viruses. The symptoms, severity, and length of disability attributed to influenza are variable. Infections with an influenza virus occur in about one of every six adults annually with half seeking medical attention. Children are affected more than adults are.

The influenza virus is highly contagious. Spread occurs through airborne respiratory droplets. Influenza occurs more frequently and severely in smokers. It strikes hardest with the highest morbidity and mortality in the elderly and in those with chronic medical conditions. Individuals with asthma, chronic bronchitis, chronic obstructive pulmonary disease (COPD), emphysema, chronic heart disease, diabetes, kidney dysfunction are prone to complications of influenza, as are individuals who are immunosuppressed. Although all persons can benefit from annual immunization against influenza (annual flu shots), it is imperative that the people at highest risk receive the vaccination annually without fail. The influenza viruses (types A and B) mutate frequently, consequently influenza vaccines are changed annually in anticipation of the expected predominate strain(s).

Influenza is well known as a cause for epidemics in closed groups such as schools and nursing homes, as well as entire communities or whole countries. Occasionally, there are worldwide pandemics; the most recent pandemics occurred in 1957, 1968, and 1977; all began in mainland China. Epidemics in temperate climates occur during the winter months; however, in tropical climates, they can occur at any time. About one in 1,500 persons with an underlying disease die from the complications of influenza.

How is it diagnosed?

History: Common to almost all cases of influenza are fever and systemic symptoms followed by upper and lower respiratory symptoms several days later. Individuals may report an abrupt onset of fever, chills, headache, muscle aches, joint pain, and fatigue. When the systemic symptoms somewhat subside, respiratory symptoms become dominant. The respiratory symptoms are caused by the virus invading the cells lining the tracheobronchial tree. This causes pain, swelling and sloughing of dead cells. This sloughing promotes the characteristic cough of influenza and the dead cells are prime targets for bacterial pneumonia.

Physical exam Fever of 101 F to 104 F is common. The individual appears quite ill. The skin is warm, and flushed, and eyes are glassy and/or watery. The mucous membranes of the nose and throat appear reddened but generally are free of drainage. Often lymph nodes in the neck will be slightly swollen. Examination of the lungs usually reveals just a few scattered abnormal sounds. Significant changes such as diminished breath sounds as well as other signs of lung disease may indicate pneumonia.

Tests: A chest x-ray is indicated in individuals who are at high risk of developing pneumonia, such as individuals with COPD, the elderly and the immunosuppressed, or in the individual with abnormalities detected on physical exam.

How is Influenza treated?

Treatment is primarily symptomatic in most cases and includes rest, fluids, analgesics, antipyretics (fever reducing medications), and cough suppressants, if necessary. Antibiotics are not warranted unless a bacterial infection is suspected.

Medications

Ilosone (Erythromycin), Symmetrel (Amantadine), Tamiflu (Oseltamivir)

Activity

Rest is the best medicine. If you are in good general health, rest helps your body fight the virus.

Diet

• Appetite is usually lacking. You may just want liquids at first, then progress to small meals of bland starchy foods (dry toast, rice, pudding, cooked cereal, baked potatoes).
• Drink at least 8 glasses of water a day (especially if you have a high fever). Extra fluids, including fruit juice, tea and noncarbonated drinks, also help thin lung secretions.

What might complicate it?

Three types of pneumonia can occur as complications to influenza. They are viral, bacterial, and mixed viral and bacterial. Influenza viral pneumonia occurs most frequently in individuals with underlying pulmonary or cardiac disease and in those who are immunosuppressed. It has a rapid, debilitating onset that can require hospitalization. If the pneumonia worsens, it can result in respiratory failure and death. The mortality rate is close to fifty percent.

Secondary bacterial pneumonia follows a different course. It affects mostly the elderly and those with chronic medical diseases. Generally, an individual diagnosed with influenza will be improving for three to four days when there is a resurgence of symptoms. Bacterial pneumonia can be treated with antibiotics.

Mixed viral and bacterial pneumonia generally involves a milder form of viral pneumonia combined with a bacterial pneumonia. The condition will respond at least partially to antibiotic therapy. Other non-pulmonary complications are rare in adults but can occur. A few of these are Reye's syndrome, toxic shock, meningitis, and inflammation of the heart muscle or lining.

Predicted outcome

In healthy young and middle-aged adults, full recovery from influenza with no residual effects can be expected in a matter of days or weeks. In older adults and those with underlying pulmonary and cardiac disease, the outcome may leave them in a partially disabled condition by worsening their underlying chronic disease process. In influenza complicated by bacterial pneumonia, full recovery is expected in healthy young and middle-aged adults. Those who might contract the more serious primary viral influenza pneumonia are at risk of prolonged disability and, if hospitalized in respiratory failure, there is a mortality rate of fifty percent.

Alternatives

It may be difficult to distinguish a case of influenza from other upper and lower respiratory tract diseases, especially early and late in the flu season. Mycoplasma and chlamydial pneumonia may produce the same syndrome as well as a number of other viral and bacterial infections.

Appropriate specialists

Internist, pulmonologist, infectious disease specialist.

Last updated 4 April 2018