Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Influenza, commonly called "the flu," is caused by viruses
that infect the respiratory tract.
Influenza viruses are divided into three types, designated A, B, and
C, with influenza A types usually causing the most problems in humans.
Most people who get the conventional or seasonal flu recover completely in one to two weeks, but
some people develop serious and potentially life-threatening medical
complications, such as pneumonia.
Much of the illness and death caused by conventional or seasonal influenza can be prevented by
annual influenza vaccination.
Influenza A undergoes frequent antigenic changes that require new vaccines to be developed and people to obtain a new vaccination every year. New vaccine technology is being developed.
In April 2009, a new flu virus termed novel H1N1 swine flu developed in
Mexico, rapidly spread worldwide, and caused the WHO to declare a flu pandemic.
Eventually, the WHO declared the pandemic over in 2010. In 2012, a new type of flu strain developed, H3N2v, but has not developed into any epidemic situations currently.
Like the influenza virus, drug treatments are constantly changing and improving, but currently, timely vaccination is still considered to be the best defense against the flu. However, the CDC considers antivirals an important adjunct to flu vaccine in the control of the disease process.
People should be aware that flu pandemics can cause severe flu symptoms and sometimes death in many individuals who may be more susceptible to the pandemic flu than the conventional flu; however the previous pandemic flu virus (H1N1) has been available in vaccines and is considered part of the conventional circulating flu viruses.
Individuals should check with their doctors to determine if they are considered to be at higher risk of getting severe flu symptoms than the normally healthy population.
Picture of the influenza virus
What is influenza?
Influenza, commonly called "the flu," is an illness caused by RNA viruses that infect the respiratory tract of many animals, birds, and humans. In most people, the infection results in the person getting fever, cough, headache, and malaise (tired, no energy); some people also may develop a sore throat, nausea, vomiting, and diarrhea. The majority of individuals has symptoms for about one to two weeks and then recovers with no problems. However, compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection can cause a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus.
The above is the usual situation for the yearly occurring "conventional" or "seasonal" flu strains. However, there are situations in which some flu outbreaks are severe. These severe outbreaks occur when a portion of the human population is exposed to a flu strain against which the population has little or no immunity because the virus has become altered in a significant way. These outbreaks are usually termed epidemics. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last hundred years since influenza virus was identified in 1933. By an examination of preserved tissue, the worst influenza pandemic (also termed the Spanish flu or Spanish influenza) occurred in 1918 when the virus caused between 40-100 million deaths worldwide, with a mortality rate estimated to range from 2% to 20%.
In April 2009, a new influenza strain against which the world population has little or no immunity was isolated from humans in Mexico. It quickly spread throughout the world so fast that the WHO declared this new flu strain (first termed novel H1N1
influenza A swine flu, often later shortened to H1N1 or swine flu) as the cause of a pandemic on June 11, 2009. This was the first declared flu pandemic in 41 years. Fortunately, there was a worldwide response that included vaccine production, good hygiene practices (especially hand washing) were emphasized, and the virus (H1N1) caused far less morbidity and mortality than was expected and predicted. The WHO declared the pandemic's end on Aug. 10, 2010, because it no longer fit into
the WHO's criteria for a pandemic.
Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until the virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children, and it occasionally causes
ear, eye,
sinus, joint, and a few other infections,
but it does not cause the flu.
Reviewed by Melissa Conrad Stöppler, MD on 2/20/2013
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Influenza, or the "flu," is a illness of the breathing
system (respiratory system) and muscles caused by a virus. While a vaccine is
available to prevent the flu, its effectiveness varies according to the degree
of match between the viral strains used to prepare the vaccine and those strains
actually in circulation in a given year. Not everyone receives the flu vaccine, and even
some of those who do can develop symptoms of the flu.
Mild cases of the flu may seem like common colds. But most cases of the flu
can be distinguished from colds because the symptoms (cough, muscle aches and
pains, sore throat, fatigue, and headache)
are more severe than those of the common cold. Flu symptoms also tend to occur suddenly and include high fevers
(temperatures of 101 degrees F or more).
Headaches can be divided into two categories: primary headaches and secondary headaches. Migraine headaches, tension headaches, and cluster headaches are
Bronchitis is a disease of the respiratory system in which the bronchial passages become inflamed. There are two types of bronchitis, acute and chronic.
Herpes simplex infections are common and when they appear around the mouth and lips, people often refer to them as "cold sores" and "fever blisters." Canker
Chronic bronchitis is a cough that occurs daily with production of sputum that lasts for at least three months, two years in a row. Causes of chronic bronchitis
Fatigue can be described in various ways. Sometimes fatigue is described as feeling a lack of energy and motivation (both mental and physical). The causes
Novel H1N1 influenza A virus infection (swine flu) is an infection that generally is transferred from an infected pig to a human, however there have been
Plague is an infectious disease caused by the Yersinia pestis bacteria, which is primarily found in rodents the fleas that feed off of them. The bacteria
Reye's syndrome (RS, or Reye syndrome) is a sudden, sometimes fatal, disease of the brain with degeneration of the liver. Reye syndrome occurs in children
The most common taste disorder is phantom taste perception; that is, a lingering, often unpleasant taste even though you have nothing in your mouth. We
Adenovirus infection, particularly Ad14, or the "killer cold virus" has been on the increase in the past two years. Symptoms range from those experienced
Drug resistance (antimicrobial resistance) is the ability of bacteria, fungi, parasites, and viruses to grow, even in the presence of a drug that would
Before treating a cold, the flu, or allergies with over-the-counter (OTC) medications, it's important to know what's causing the symptoms, which symptoms
Bioterrorism is a form of terrorism where there is the intentional release of biological agents such as viruses, germs, or bacteria. Diseases caused by
Severe acute respiratory syndrome (SARS) is a respiratory disease caused by the coronavirus SARS-CoV. Symptoms include fever and shortness of breath. Patients
Exercise-induced asthma is asthma triggered by vigorous exercise. Symptoms include coughing, shortness of breath, chest tightness, wheezing, and fatigue
If you have a COPD such as emphysema, avoiding chronic bronchitis and colds is important to avoid a more severe respiratory infection such as pneumonia.
Pregnant and women who are breastfeeding are encouraged to receive the seasonal flu shot as well as the 2009 H1N1 influenza (swine flu) vaccine. H1N1 flu
