Influenza (Flu) - Provider Information

Influenza usually comes on suddenly, one to four days after the virus enters the body, and may include these symptoms:

• Fever or feeling feverish/chills
• Cough
• Sore throat
• Runny or stuffy nose
• Headache
• Muscle or body aches
• Tiredness (can be extreme)

Among children, otitis media (ear infection), nausea, vomiting, and diarrhea are common. Some infected persons are asymptomatic.

Influenza-like illness, or ILI, is defined as fever ≥100°F AND cough and/or sore throat (in the absence of a known cause other than influenza).

Human to Human

Influenza viruses are spread from person to person by respiratory droplets generated when an infected person coughs, sneezes, or talks in close proximity to an uninfected person. Sometimes, influenza viruses are spread when a person touches a surface with influenza viruses on it (e.g., a doorknob), and then touches his or her own nose or mouth.

Most healthy adults who are ill with influenza may be able to infect other people beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children and persons with weakened immune systems might be able to infect other people for even a longer period of time.  The virus can also be spread by people who are infected but have no symptoms.

Influenza A Viruses Between Animals and Humans

Influenza A viruses normally seen in one species sometimes can cross over and cause illness in another species. Influenza viruses from different species can mix and create a new influenza A virus if viruses from two different species infect the same person or animal. For example, if a pig were infected with a human influenza virus and an avian influenza virus at the same time, the viruses could reassort (exchange genetic material) and produce a new virus. The resulting new virus might then be able to infect humans and spread from person to person, but it would have surface proteins not previously seen in influenza viruses that infect humans. Most people would have little or no immunity against this type of major change in the influenza A virus. If this new virus caused illness in people and was transmitted easily from person to person, an influenza pandemic could occur. It also is possible that the process of reassortment could occur in a human. For example, a person could be infected with an avian influenza strain and a human strain of influenza at the same time. These viruses could reassort to create a new virus that had a protein from the avian virus and other genes from the human virus. While it is unusual for people to get influenza infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and pig influenza A viruses have been reported.

Most people generally recover from illness in a few days to less than two weeks, but some people develop complications (such as pneumonia) and may die from influenza. The highest rates of influenza infection occur among children; however, the risks for serious health problems, hospitalizations, and deaths from influenza are typically greatest among people 65 years of age or older, children aged <5 years especially those aged <2 years, pregnant women, and people of any age who have medical conditions that place them at increased risk for complications from influenza.

In people with chronic medical conditions such as heart or lung disease, influenza can lead to pneumonia and other life-threatening illnesses. Persons 65 years of age and older account for approximately 90% of deaths attributed to pneumonia and influenza. Young children with influenza can develop high fevers, and a small percentage of children hospitalized with influenza can have febrile seizures. Deaths from influenza are uncommon among children, but do occur. Influenza has also been associated with neurological problems, Reye’s syndrome, muscle inflammation, and heart inflammation.

Most people who develop influenza illness will recover on their own by getting rest and will not need medication. Antiviral medications can shorten the duration and severity of illness if given within the first 48 hours of the illness. These medications are usually prescribed to persons who have a severe illness or to those who are at higher risk for developing serious illness or complications due to influenza.

The best way to prevent influenza is to get an influenza vaccine each year as soon as the vaccine is available to the public. Vaccination is associated with reductions in influenza-related respiratory illness and physician visits among all age groups, hospitalizations, and deaths among persons at high risk, otitis media (ear infection) among children, and work absenteeism among adults.

Other forms of prevention include:

• Hand washing and using alcohol-based hand sanitizers,
• Covering your coughs and sneezes with a disposable tissue or your arm or sleeve,
• Avoiding touching your eyes, nose, or mouth,
• Avoiding close contact with persons who are ill,
• Staying home when you are ill, and
• Taking antiviral medications if prescribed by your doctor.
  • In certain situations (e.g., influenza outbreaks in settings like nursing homes), antiviral medications may be prescribed to high-risk individuals to prevent them from developing influenza illness after exposure to infected individuals.

• Influenza, General Investigation Form (PDF), 35KB, September, 2011)
• Influenza, Supplemental Investigation Questions (PDF), 42KB, September, 2011)

Individual cases of influenza are not reportable by law in Texas.  State, regional, and local health departments rely on volunteer clinics, hospitals, laboratories and others to report influenza data throughout the season.  However, there are situations where influenza becomes reportable by state law.  These situations are:

• Influenza-associated pediatric mortality cases are reportable within one working day.
• Novel or variant influenza cases are reportable immediately. 
• Influenza-like illness (ILI) or influenza-associated outbreaks in any setting are reportable immediately. 

All influenza-associated pediatric mortality cases, novel/variant influenza cases, and ILI/influenza-associated outbreaks should be reported to the local health department or health service region.

Several Texas laws (Tex. Health & Safety Code, Chapters 81, 84 and 87) require specific information regarding notifiable conditions be provided to the Texas Department of State Health Services (DSHS). Health care providers, hospitals, laboratories, schools, and others are required to report patients who are suspected of having a notifiable condition (25 Tex. Admin. Code §97.2).

Information for the Public

• Visit the CDC's Influenza Antiviral Medications web site.

Information for Health Care Professionals

• Visit the CDC's Influenza Antiviral Medications: Summary for Clinicians website.

Influenza viruses that infect birds are called “avian influenza viruses”. Only influenza A viruses infect birds. All known subtypes of influenza A viruses can infect birds, except subtypes H17N10 and H18N11, which have only been found in bats; however, there are substantial genetic differences between the subtypes that typically infect both people and birds. Although avian influenza A viruses do not usually infect humans, several instances of human infections and outbreaks of avian influenza have been reported since 1997. Most cases of avian influenza infection in humans are thought to have resulted from contact with infected poultry or contaminated surfaces. There is still a lot to learn about how different subtypes and strains of avian influenza viruses might affect humans. Because of concerns about the potential for more widespread infection in the human population, public health authorities closely monitor outbreaks of human illness associated with avian influenza. To date, human infections with avian influenza viruses detected since 1997 have not resulted in sustained human-to-human transmission. However, because influenza viruses have the potential to change and gain the ability to spread easily between people, monitoring for human infection and person-to-person transmission is important.

From December 2014 to June 2015, the United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) and the U.S. Department of the Interior (DOI), National Wildlife Health Center detected and reported highly pathogenic avian influenza (HPAI) H5 viruses in U.S. domestic poultry (backyard and commercial flocks), captive wild birds, and wild birds. The HPAI H5 influenza A viruses detected in US domestic poultry, captive wild birds and wild birds were H5N8, H5N2, and a new H5N1 virus that had a combination of genes from HPAI H5N1 viruses that spread in Asia and low-pathogenic avian influenza viruses that circulate in wild birds in North America. No human infections with these viruses were detected; however, similar viruses have infected people.

As of June 15, 2017, 859 laboratory–confirmed avian influenza A (H5N1), not the newly detected H5N1, infections in humans resulting in 453 deaths have been reported to the World Health Organization (WHO) from 16 countries. No human infections with avian influenza A (H5N1) have been identified in the United States. For updates on avian influenza, visit the CDC's Information on Bird Flu website and the WHO's Influenza (Avian and other zoonotic) website.

There has also been avian influenza (not H5N1) outbreaks reported in the US.  In January 2016, an outbreak of HPAI (H7N8) virus was reported in a commercial turkey flock in Dubois County, Indiana. 

Low pathogenic avian influenza (LPAI) (H7N8) was subsequently detected in eight nearby turkey flocks. No transmission of HPAI (H7N8) or LPAI (H7N8) virus to humans was reported.

Two outbreaks of high pathogenic avian influenza (HPAI) (H7N9) were reported in Lincoln County, Tennessee in March 2017. In addition, five states, Georgia, Wisconsin, Tennessee, Alabama and Kentucky, reported cases of low pathogenic avian influenza (LPAI) (H7N9) during 2017. One outbreak of LPAI (H5N2) was reported in Wisconsin in 2017. 

In addition, two avian influenza (not H5N1) outbreaks occurred among poultry populations in southeast and northeast Texas in February and May 2004, respectively. No human cases of influenza occurred from these poultry outbreaks.

In April 2013, China began reporting human cases of avian influenza A (H7N9). As of June 15, 2017, there have been 1533 laboratory-confirmed cases of avian influenza A (H7N9), including at least 592 deaths, reported to the World Health Organization. Most human cases are associated with exposure to infected live poultry or contaminated environments, including markets where live poultry are sold. Information to date suggests that these viruses do not transmit easily from human to human.

In December 2016, New York City detected cases of avian influenza A (H7N2) among cats in an animal shelter. There was one confirmed human case associated with the outbreak. The person had mild symptoms and recovered. There were no cases of person-to-person transmission reported.

View the latest information on influenza surveillance for the current influenza season and past influenza seasons in Texas may be found on the DSHS Influenza Survelliance webpage.

Children with influenza are required to be excluded from school and daycare for at least 24 hours after fever has subsided without the use of fever suppressing medications. It is recommended that adults with influenza not return to work for at least 24 hours after fever has subsided without the use of fever suppressing medications.

The official influenza reporting season for the United States begins in October and continues through May. In Texas, influenza activity usually peaks in January or February, although the peak of influenza has happened as early as October and as late as March. Individual cases of influenza are not tracked; however, sentinel surveillance partners in the state provide information on when and where influenza viruses are circulating, if circulating influenza viruses match the vaccine strains, if the circulating influenza viruses are changing, where and when influenza-like illnesses are occurring, and the severity of influenza activity. For surveillance reports see the Data link above.