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Influenza Testing, Diagnosis, Treatment & Prevention

Influenza can be difficult to diagnose through clinical symptoms alone because so many of the symptoms are similar to other infectious respiratory illnesses.   A thorough history and physical examination can often diagnose influenza.  Examination of the nose may show nasal drainage and swelling of mucous membranes.  The throat exam may show redness or post nasal drainage.   The ears are examined for fluid or blockage.  Exam of the chest may show increased respiratory and heart rate (usually due to fever).  If secondary bacterial infection such as pneumonia is present, the lungs may have fluid and this can be detected by examination of the chest or a chest x-ray may be needed.  Oxygen levels can be checked with a pulse oximeter – a device used to measure oxygen levels from the fingertip.

The most important test in detecting influenza are nasal cultures.  There are quick tests that can be done in the doctor’s office as well as longer cultures that take 3-10 days.  These tests need to be performed within the first 4 days of illness.   A swab is inserted into the nose to obtain the sample.  Some tests require irrigation of the nose with saline and drainage is then blown into a sample container and sent to the lab.  The longer term tests generally aren’t used since the rapid tests can provide 50-70% accuracy in detecting influenza infection. Physicians’ offices often perform the rapid tests especially during peak influenza activity.

If influenza is complicated by secondary bacterial infections such as pneumonia, ear infection or sinusitis, more tests may be needed.   This could include a chest x-ray or CT scan, sinus x-ray or CT scan and blood work.  A complete blood count may show an elevated white count when secondary bacterial infection is present.  Viral infections such as the flu may cause a low white count.  A metabolic panel checks for imbalances in electrolytes (potassium, sodium) from fluid loss due to fever, vomiting or diarrhea and is useful to check for dehydration.  Urinalysis can also detect dehydration signs.

A physician’s knowledge of the number of influenza cases in the area is important in understanding the results and interpreting whether a false positive is expected (beginning and end of influenza season) or a false negative is expected (height of influenza season). This knowledge can allow the physician to determine whether a viral culture will be necessary or if empiric treatment should be started (presuming there is influenza infection based on signs and symptoms even if testing is negative).


Influenza is usually diagnosed and treated in your primary doctor’s office or urgent care center.  If the influenza tests come back positive or there is a high index of suspicion of influenza, several treatments can be started.  Symptomatic care with increased intake of fluids, Tylenol® or fever-reducing medications and rest are usually recommended.  Generally a physician will start with an antiviral prescription in order to fight the infection.  These differ from antibiotics which treat bacterial infections. Most often these antivirals are used for those with high risk conditions to minimize the severity of the infection. Antiviral drugs can lessen the symptoms and shorten the time of sickness by 1 to 2 days as well as minimize some of the most serious flu complications. For best effects the antiviral drug treatment should begin within 48 hours of symptoms.   Some common side effects of antiviral medications can be nausea, vomiting, allergic reactions, confusion, diarrhea and flu-like symptoms.

If secondary bacterial infections such as pneumonia, sinusitis or ear infections occur, antibiotics are typically prescribed.  If a patient requires hospitalization intravenous antibiotics are sometimes used as well as other supportive care.

Influenza in a healthy adult typically runs its course with or without treatment. If you are in close contact with someone with influenza you can be treated with antiviral medication to prevent flu.  Anyone with pre-existing health conditions, should contact their healthcare provider to find out if treatment is indicated for flu exposure.  The elderly or very young need to be monitored more closely for complications if they are diagnosed with influenza or are exposed to someone close who has been diagnosed with the flu.  Sometimes hospitalization is required to manage a patient with influenza especially if there are other complicating medical conditions. Consultation with an infectious disease (a doctor who is an expert on influenza and its secondary complications) may be needed.


The best method of treatment is still preventive vaccination every year.  The CDC recommends flu vaccination for the following individuals:

Children aged 6 months–4 years (59 months). People 50 years and older People with chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus). People who are immunosuppressed (including immunosuppression caused by medications or by human immunodeficiency virus). Women who are, or will be, pregnant during the influenza season. Children aged 6 months to 18 years receiving long-term aspirin therapy and who therefore might be at risk for experiencing Reye syndrome after influenza virus infection. Residents of nursing homes and other chronic-care facilities; American Indians/Alaska Natives. People who are morbidly obese (body-mass index is 40 or greater). Health-care personnel. Household contacts and caregivers of children aged younger than 5 years and adults aged 50 years and older, with particular emphasis on vaccinating contacts of children aged younger than 6 months. Household contacts and caregivers of persons with medical conditions that put them at higher risk for severe complications from influenza.

For adults over the age of 65 years and older the recommended vaccination consists of high dose flu vaccine.  This vaccination consists of three flu strains most likely to cause the flu during the upcoming season. The high dose vaccination, however, contains four times as much flu virus antigen in order to provide increased stimulus to the immune system for those high-risk adults. The high-dose vaccine can lead to increased chance of fever and soreness at the injection site for up to a week post-vaccination.  Regular dose flu vaccine has similar but not as severe side effects of mild flu symptoms, soreness at injection site and muscle aches.

The recommendations for vaccination of people with egg allergies have changed for 2016-2017. People with egg allergies can receive any licensed, recommended age-appropriate influenza vaccine and no longer have to be monitored for 30 minutes after receiving the vaccine. People who have severe egg allergies should be vaccinated in a medical setting and be supervised by a health care provider who is able to recognize and manage severe allergic conditions.

Some people should not be vaccinated for influenza.  The CDC advises the following people should not be vaccinated for influenza:

People who have had a severe reaction to an influenza vaccination, Children younger than 6 months of age (influenza vaccine is not approved for children in this age group), People who are moderately or severely ill with or without fever should usually wait until they recover before getting flu vaccine. If you are ill, talk to your doctor about whether to reschedule the vaccination. People with a mild illness can usually get the vaccine.

A history of Guillain-Barré Syndrome (GBS) within 6 weeks following receipt of influenza vaccine is a precaution for the use of influenza vaccine.

The best way to prevent contracting influenza is to get vaccinated each year.  Other good health habits can reduce your risk of contracting and spreading the flu.  Avoid close contact with people who are sick. If you are sick, stay away from others to protect them from getting sick too.  You can prevent others from catching the flu if you stay home from work, school, and errands when you are sick. Cover your mouth and nose with a tissue when coughing or sneezing.  Washing your hands often will help protect you from germs. If soap and water are not available, use an alcohol-based hand rub. Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.  Clean and disinfect frequently touched surfaces at home, work or school, especially when someone is ill.  Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, eat nutritious food and avoid smoking cigarettes.


Prognosis for influenza is good but in patients 65 years and older or those with other health conditions complications may occur. The people most vulnerable to infection are children younger than 5, adults over the age of 65, morbidly obese individuals, and American Indians/Alaska Natives. Those with asthma, diabetes, heart disease, cancer, HIV/AIDS and pregnant women are also considered high risk groups and should be vaccinated every year in addition to taking precautions against exposure beyond ordinary measures. Anyone with chronic medical conditions should take extra special care since influenza can worsen those conditions and lead to an increased chance of death and longer period of sickness.

Susan Puckett, PA-C, ENT and Internal Medicine