Influenza outbreaks occur each winter at an annual cost of $12 billion to $71 billion in the United States alone, reports Harvard Medical School professor Dr. Raphael Dolin in “Harrison’s Principles of Internal Medicine.” An epidemic—as public health authorities initially feared 2009 H1N1 would prove to be—could cost up to $167 billion. The clinical syndrome of influenza—a constellation of fever, dry cough, muscle pain and other symptoms—has three basic causes: exposure to an infected person, contact with contaminated objects and exposure to infected animals.
Exposure to Infected Person
The main cause of influenza is exposure to an infected person, say the Centers for Disease Control and Prevention. The virus aerosolizes in respiratory secretions or “droplets” which a cough or sneeze can propel up to three feet away. Physical contact need not occur, although contact activities such as kissing or even touching hands with an infected person can obviously also cause infection. Unfortunately, people who exhibit no signs or symptoms can still spread the disease. The influenza virus appears in secretions approximately one day before an infected person exhibits symptoms and for a few days after they recover, although the highest levels are found when the person is actively sick.
Contact With Contaminated Objects
Objects are said to be contaminated with the influenza virus because they don’t get sick themselves, even though they cause sickness in people. Respiratory droplets that land on linens, eating utensils, and even door handles or telephone receivers can all cause infections. In some cases, contaminated objects make direct contact with the mouth or nose, triggering infections. In other cases, the hands serve as an intermediary, which is why the CDC recommends frequent hand washing as one of the good health habits that can help prevent influenza.
Exposure to Infected Animal
Influenza viruses also circulate widely among animals, including ducks, chickens, pigs, whales, horses and seals, notes the CDC. Influenza caused by exposure to infected animals follows the same patterns as exposure to infected people and contaminated objects, although it occurs far less frequently. Unfortunately, exposure to an infected animal often causes severe disease because humans possess fewer antibodies to influenza viruses they encounter infrequently. Swine flu and bird flu provide excellent examples of influenza causes by exposure to infected animals.
References
- “Harrison’s Principles of Internal Medicine, 17th edition;” A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longer, J.L. Jameson and J. Loscalzo (Eds.); 2008
- CDC: Transmission of Influenza Viruses from Animals to People
- CDC: Questions and Answers: Seasonal Influenza
- CDC: Seasonal Influenza: The Disease
- CDC: CDC Says "Take Three" Actions to Fight Flu
