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Flu Information

Influenza (the flu) is a contagious respiratory illness caused by the influenza virus.  The flu season in the U.S. usually starts in the late fall, peaks in January/February, and continues through the early spring.


Most experts believe that influenza is transmitted (up to 6 feet) from an infected person’s cough or sneeze. Virus-laden respiratory droplets from an infected sneeze can be inhaled through the nose or mouth of nearby persons. These respiratory droplets only remain suspended in the air a few seconds and then settle on environmental surfaces, where they remain viable for minutes to hours. A less common method of transmission is when a person touches a contaminated environmental surface and then inoculates their eye/nose/mouth with the virus. For these reasons, it is important to use proper respiratory etiquette with all coughs/sneezes, as well as proper hand washing precautions.

Once the virus enters the body, it usually incubates 2-3 days before clinical symptoms develop. Adults can shed influenza virus the day before symptoms begin, but are most contagious the first 3-5 days of clinical illness, with most shedding complete by day 7. Children and immunocompromised adults can shed the virus ≥ 10 days.


The influenza virus causes a broad spectrum of clinical illness that varies in severity and duration amongst different individuals. Influenza infection shares many of the same symptoms as the common cold (sore throat, cough, runny nose), but the systemic symptoms (fever, chills, muscle aches) are classically more abrupt and severe with influenza.   A small percent of individuals do not experience the classic high fever, severe muscle aches, and fatigue.

Flu Symptoms (most experience some or all of these symptoms):

  • Fever
  • Cough
  • Sore throat
  • Runny nose
  • Muscle aches
  • Headache (Generalized)
  • Fatigue
  • Diarrhea and vomiting (infrequent – mainly in young children).
  • Duration of Influenza Infections
  • Uncomplicated influenza illness typically resolves after 3–7 days for the majority of persons, although cough and malaise can persist for >2 weeks.

Populations at Higher Risk for Medical Complications from Influenza

  • Children <5 years,="" but="" especially=""><2>
  • Adults ≥65 years of age

Persons with medical conditions including:

  • Chronic lung disease (e.g. chronic obstructive pulmonary disease, asthma, and cystic fibrosis)
  • Heart disease (except hypertension)
  • Kidney disorders
  • Liver disorders
  • Blood disorders (including sickle cell disease)
  • Endocrine disorders (including diabetes mellitus)
  • Metabolic disorders (including inherited metabolic disorders and mitochondrial disorders)
  • Neurologic and neurodevelopmental conditions (including cerebral palsy, epilepsy, stroke, intellectual disability [mental retardation], moderate to severe developmental delay, muscular dystrophy, and spinal cord injury)
  • Immunosuppression due to disease or medications (including HIV, cancer, and chronic glucocorticoids)
  • Women who are pregnant or postpartum (within two weeks after delivery)
  • Children and adolescents <19 years="" of="" age="" and="" receiving="" long-term="" aspirin="">
  • Native Americans and Alaskan Natives
  • Extremely obese (body mass index [BMI] ≥40)
  • Residents of nursing homes and other long-term care facilities


During known flu outbreaks, most patients can be diagnosed on clinical grounds based on signs and symptoms.   Acute onset of Fever ( ≥ 100.0) and Cough/Sore Throat has a diagnostic positive predictive value (79%-88%) for the flu when influenza is confirmed to be circulating in the community.  Sporadic cases of influenza can occur throughout the year;  during non-epidemic times of the year, diagnosis based on clinical findings is not accurate because influenza shares signs/symptoms with many other infectious conditions.  

Laboratory diagnostic testing includes Nucleic Acid Testing (Highly Sensitive, Highly Specific, Expensive), Digital Immunoassay (Moderately High Sensitivity, High Specificity, Moderately Expensive), Rapid Flu Antigen Detection Tests (Low to Moderate Sensitivity, High Specificity, Inexpensive, Can be done in office).
Lab Testing for Influenza should be considered for the following groups:

Persons who are in the high risk groups (see above) for developing complications from the flu.
Healthcare workers (staff, students) with acute flu-like symptoms who present within 5 days of symptom onset during a known influenza outbreak.
Persons experiencing flu-like symptoms during times of the year where there is low flu activity (to reduce unnecessary antibiotic/antiviral medication use, reduce unnecessary lab/radiology, initiate necessary Infection Control Measures when flu present).


Most healthy individuals who are not in a high risk group will recover from the flu within a week. Since most healthy individuals with the flu will recover uneventfully, there are no recommendations for testing or treatment in these groups.  Testing and treatment of healthy individuals can be considered on an individualized basis (e.g. testing and/or treatment of healthcare workers or caregivers should be considered to prevent spread of influenza to the vulnerable population they serve).

Antiviral Medication (Neuraminidase Inhibitors -  Oseltamivir, Zanamivir, Peramivir) – if initiated within 1-1.5 days of symptom onset, antiviral medications are moderately effective at reducing the severity and duration of influenza infections.  While there is little to no benefit if the treatment is initiated after 48 hours from symptom onset in healthy individuals, there is evidence to suggest that antiviral therapy may decrease complications from the flu in individuals in high risk groups (see above).  Therefore, most experts recommend antiviral therapy at any point in the illness for individuals with: (1) influenza requiring hospitalization (2) complicated, severe influenza infection (3) high risk (see high risk groups above) for influenza complications.

Analgesics/Antipyretics – Acetaminophen or other nonsteroidal anti-inflammatory medications can be used to treat fever, headache, sore throat, and muscle aches associated with the flu.   Salicylates (Aspirin) should be avoided in children below age 18 due to its association with Reye Syndrome.
Hydration – febrile illnesses increase the body’s fluid losses, so maintaining hydration is recommended.  Drink enough fluid for the urine to run clear to pale yellow.  

Reducing the Spread of Infection

It is essential that all individuals with the signs/symptoms of the flu do the following:
Stay Home. Avoid spreading the infection to family, colleagues, and patients.  If symptoms begin while at school, students should report their symptoms to their college and go home.   Students engaged in clinical activities should immediately stop patient care activities, wear a face mask, report their symptoms to their immediate supervisor, and remove themselves from the clinical site.
Call for an Appointment (843-792-3664) if you are in a high risk group and are experiencing flu symptoms, or feel that your symptoms warrant medical attention. To protect the safety of your classmates, DO NOT WALK INTO STUDENT HEALTH WITHOUT AN APPOINTMENT. Individuals who are experiencing flu symptoms will be required to wear a mask in the waiting area. When necessary, arrangements will be made for an alternate entrance to Student Health Services clinic.

Infection Control Measures include:

  • Cough Etiquette - Covering your nose and mouth with a tissue or with the crook of your elbow when you cough or sneeze. Throw the tissue in the trash after you use it.
  • Wash your hands often with soap and water, especially after you cough or sneeze. You can also use an alcohol-based hand cleaner.
  • Avoid touching your eyes, nose or mouth.
  • Try to avoid close contact with sick people.
  • Stay home if you are sick until at least 24 hours after you no longer have a fever (100°F or 37.8°C) or signs of a fever (without the use of a fever-reducing medicine, such as Tylenol®).  

Students who have clinical activities with patient contact are required to stay home for seven days after the onset of flu symptoms.

While sick, limit contact with others as much as possible to keep from infecting them.

Seek medical attention at the EMERGENCY ROOM if you have flu symptoms (high fever and cough) accompanied by:

  • Difficulty breathing or shortness of breath.
  • Pain or pressure in the chest or abdomen.
  • Sudden dizziness.
  • Confusion.
  • Severe or persistent vomiting.
  • Flu–like symptoms that improve but then return with fever and worse cough.

Prevention of the Flu

The best protection from the flu is to receive the annual flu vaccine. While receiving the vaccine will not guarantee you will not get the flu, it lessens the severity and duration of illness in most of those who do become ill.

In 2010, the US Advisory Committee on Immunization Practices expanded the recommendation for influenza vaccination to include all individuals 6 months of age and older. High risk individuals, their close contacts, and healthcare workers remain high priority populations to receive flu vaccination.   Healthcare workers are more likely to be exposed to influenza and immunization is important to protect their personal health, as well as the vulnerable population they serve.  Immunization coverage of healthcare workers is 97% when mandated by their employer, but falls to 46% when immunization is not required.  Flu vaccination is mandatory for MUSC Hospital staff and for almost all the colleges. 

The influenza virus has a high rate of mutation and immunity from infection or vaccination does not confer long lasting protection. Because inactivated vaccines take approximately 6 months to manufacture, each year’s flu vaccine is comprised of the predominant flu strains at the end of the previous flu season.  The protective efficacy of the influenza vaccine is determined by how well the predicted influenza strains of the vaccine “match” the circulating strains of virus circulating during the flu season. The influenza vaccine provides up to 80% protection in healthy individuals when the vaccine is a good “match”. The influenza vaccine is less effective in the population groups that are most susceptible to complications of the flu (the young, the elderly, and persons with weakened immune systems due to chronic illness). Due to poor vaccine effectiveness, the Advisory Committee on Immunization Practices (ACIP) recommends that the Live Attenuated Influenza Vaccine/LAIV (FluMist) not be used.  

Contrary to popular myth, the flu vaccine cannot cause the flu. The most common adverse effect is mild arm soreness at the injection site. The immune response to the flu vaccine can often cause a low grade fever and mild systemic symptoms for 8 to 24 hours, which can be mistaken for an infection. Protective antibodies usually appear 2 weeks after the flu vaccine.  So it is also possible that one can acquire a respiratory infection in the 1-2 weeks after getting the flu shot, which can misattributed to being caused by the vaccine.

Flu Resources

More information and resources can be found at