The Call-On-Doc Guide to the Flu

Published on Sep 26, 2023 | 4:05 PM

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Every year, millions of Americans get sick, go to the doctor, and suffer hospitalizations all because of influenza.  The virus, most commonly referred to as the flu, comes in multiple variations and has been the source of many global epidemics. One exceedingly deadly pandemic caused by influenza came in the form of the Spanish flu. Ravaging the public in 1918 and 1919, the virus would go on to take the lives of 21 million Americans. Put into perspective, that’s more than WW1, WW2, the Korean War, and the Vietnam War combined. (1) Thanks to advancements in modern medicine, flu CDC statistics show significantly reduced deaths in spite of how influenza spreads.

In recent years of high influenza spread, the flu CDC statistics for flu deaths by year resulted in: 







29 million 

41 million

29 million

36 million






In the case of 2020 to 2021, the CDC admits that flu cases were so low that they would not be recorded. (2) While the numbers vary wildly year by year, the evidence shows that influenza mortality rates have improved in the United States despite how aggressively the flu spreads. Initiatives that may have helped reduce the rates include educating people about the flu virus, best practices, and prevention methods.

What is the main cause of flu?

As a disease that infects a large percentage of Americans every year, the flu is known to be highly contagious. What makes the flu contagious is its spread through respiratory droplets we expel when speaking, coughing, or sneezing, similar to strep throat and respiratory viruses that cause acute bronchitis and COVID-19. (3) The period a person is contaminated with the flu is around eight days, with symptoms not usually appearing until a day or so into the condition. (4) One of the best indications the flu contagious period has concluded is when the fever breaks. it is recommended to remain home an additional day after the fever has broken to reduce the transmission rate to others and improve recovery. 


What causes bacterial influenza?

The flu is not caused by bacteria but by influenza viruses. There are three main types of influenza viruses that infect humans: influenza A, influenza B, and influenza C. Along with influenza D, which affects only cattle and some other animals, these viruses belong to the Orthomyxoviridae family and can cause seasonal outbreaks alongside occasional pandemics. (5) 

What is the difference between flu A and flu B?

Flu A and B have a similar seasonal prevalence, but in the peak season of December to February, flu A is much more common. When it comes to contrasting flu A vs flu B, the two tend to be far more distinct in both their unique characteristics and how they affect people. One key difference is their genetics and how each evolves. Influenza A viruses are classified into various subtypes based on two surface proteins, hemagglutinin (H) and neuraminidase (N), resulting in subtypes like H1N1 (swine flu) and H3N2. These subtypes can mutate and create new strains, some of which may originate in animals and occasionally cause pandemics. On the other hand, Influenza B viruses does not have subtypes like Influenza A but instead are categorized by lineages of Yamagata and Victoria. (5)

While the difference in genetics might not necessarily seem important, it explains the significant difference in spread when comparing flu A vs flu B. While they both can cause an outbreak, flu A typically makes up 75% of cases and is the only one of the two currently able to cause pandemics. On top of rapidly moving from person to person, flu A also spreads between people and animals, mutating much faster and making it difficult to create a targeted flu vaccine. Flu B, on the other hand, only infects humans, being more common in children under five years of age, and generally being mild to moderate when a child is healthy. (6)

Beyond genetics and transmission, there are no specific symptoms that can reliably distinguish between Influenza A and Influenza B infections. Both flu A and B cause respiratory and systemic symptoms while varying in severity from person to person. The only way to truly tell the difference between the two, when someone is infected, is to get tested by a medical provider. 

How do you know if you got influenza?

As a contagious respiratory disease, the flu attacks the respiratory system of the human body. After inhaling infected respiratory droplets or touching infected surfaces and then touching your face, especially the nose, mouth, or eyes. (3) The range of time from when the flu enters the body to when a person feels the virus can vary, but it typically goes from one to four days. When infected with the flu, symptoms can include: 

  • Fever: A high fever, often exceeding 100°F (38°C), is a hallmark symptom of influenza. It typically comes on suddenly and is one of the first signs of the illness. A fever is the body's way of fighting off infection and can last for several days with the flu.
  • Chills and Sweats: Fever is often accompanied by chills, where you may feel intensely cold despite a high body temperature. These chills can be followed by profuse sweating as the fever breaks.
  • Muscle and Body Aches: Influenza is known for causing severe muscle and body aches. These aches can affect the entire body and are often described as feeling like you've been run over by a truck. They contribute to the overall sense of weakness and fatigue that accompanies the flu.
  • Fatigue: Profound fatigue is a common and debilitating symptom of the flu. It can leave you feeling extremely tired and weak, making it difficult to carry out daily activities.
  • Cough: A dry, hacking cough or a productive cough with phlegm can develop with the flu. The cough can be persistent and may linger after other symptoms have subsided.
  • Sore Throat: Some individuals with the flu experience a sore throat, which can range from mild irritation to more severe discomfort. It may be accompanied by pain when swallowing.
  • Headache: Headaches are a frequent complaint with the flu and can vary in intensity. They often accompany the other symptoms and contribute to the overall feeling of malaise.
  • Nasal Congestion: While not as prominent as in a common cold, the flu can cause nasal congestion, a runny nose, and sneezing in some people. These symptoms are more commonly associated with flu B than with flu A.
  • Nausea and Vomiting: Nausea and vomiting are less common symptoms of the flu but can occur, particularly in children. These gastrointestinal symptoms are often accompanied by other typical flu symptoms.
  • Diarrhea: Like nausea and vomiting, diarrhea is not a typical symptom of the flu, but it can occur in some cases, particularly in children and occasionally in adults. It may be associated with gastrointestinal upset.

What's the difference between an upper respiratory infection and the flu?

The key difference between an upper respiratory infection (URI) and the flu lies in their causative agents, severity, and symptoms. URIs, often referred to as the common cold, are typically caused by various viruses, resulting in milder symptoms such as a runny or stuffy nose, sneezing, and a sore throat, with low-grade or no fever. In contrast, the flu (influenza) is caused by specific influenza viruses, leading to more severe symptoms, including a sudden onset of high fever, severe muscle aches, fatigue, headache, dry cough, and a sore throat. The flu can last longer, be more debilitating, and can potentially result in complications like pneumonia, while the common cold tends to be a shorter and less severe illness. (7)

Are flu symptoms different from COVID-19?

Flu symptoms and COVID-19 symptoms can be quite similar, with both illnesses often causing fever, cough, fatigue, muscle aches, headache, and a sore throat. However, a distinctive symptom more frequently associated with COVID-19 is the loss of taste or smell (anosmia and ageusia, respectively). Moreover, the severity spectrum of COVID-19 is broader, with a tendency for more severe respiratory symptoms and complications such as pneumonia and acute respiratory distress syndrome (ARDS) compared to the flu. (8)

How do doctors test if you have the flu?

When it comes to getting a flu diagnosis, doctors will not necessarily rely on tests to confirm whether a patient has the virus or not. It is not uncommon for doctors to take into consideration the flu symptoms and opt for treatment without testing. (9) Such a decision is not just based on symptoms alone, but also taking into consideration the time of year or “flu season,” which occurs during the fall and winter or from October to February. (10) In the event that the case occurs outside of that time, which is possible, or when the doctor ops for a test, one of the options available to them for the patient includes:

  • Molecular Tests (PCR and NAAT): Polymerase Chain Reaction (PCR) and Nucleic Acid Amplification Tests (NAAT) are highly accurate and commonly used to diagnose the flu. These tests detect the genetic material (RNA) of the influenza virus in respiratory samples, such as nasal or throat swabs. The patient's sample is sent to a laboratory, where the genetic material is amplified and analyzed to confirm the presence of the virus. PCR and NAAT tests can identify the specific influenza subtype (e.g., H1N1 or H3N2), providing valuable information for public health monitoring.
  • Rapid Influenza Diagnostic Tests (RIDTs): These tests are quicker than molecular tests and are often performed in a healthcare provider's office or clinic. RIDTs detect influenza virus proteins (antigens) in respiratory samples taken from a nasal or throat swab. While RIDTs can provide results in about 15-30 minutes, they are less sensitive than molecular tests and may yield false negatives, especially when the flu is less common in the community.
  • Viral Culture: Viral culture involves growing the influenza virus in a laboratory setting from a respiratory sample. This method is less commonly used today due to its time-consuming nature (it can take several days) and the availability of faster diagnostic tests. However, viral culture can help identify the specific flu strain and is essential for monitoring changes in the virus over time.

Can you have the flu even if you test negative?

Yes, it is possible to have the flu (influenza) even if you test negative for the virus. The accuracy of flu tests, particularly rapid tests, can vary, and several factors can contribute to a false-negative result. Timing of the test, test sensitivity, viral variability, and the presence of other respiratory infections can all impact the test's accuracy. Additionally, individuals who have been recently vaccinated against the flu may experience milder symptoms, potentially leading to lower viral loads that fall below the test's detection threshold.

What illness mimics the flu?

  • Common Cold: Caused primarily by rhinoviruses, the common cold can produce symptoms such as a runny or stuffy nose, sneezing, cough, mild sore throat, and fatigue. These symptoms overlap with those of the flu.
  • COVID-19: In addition to fever, cough, fatigue, muscle aches, and a sore throat, COVID-19 can also present with shortness of breath, loss of taste or smell (anosmia), gastrointestinal symptoms, and severe respiratory distress, making it crucial to distinguish from the flu.
  • Respiratory Syncytial Virus (RSV): RSV primarily affects infants and young children but can also infect adults. Symptoms include coughing, fever, congestion, and wheezing, which can be mistaken for flu-like symptoms.
  • Mononucleosis (Mono): Caused by the Epstein-Barr virus (EBV), mono can lead to symptoms similar to the flu, such as fever, sore throat, swollen lymph nodes, fatigue, and body aches. Mono is often referred to as the "kissing disease" due to its mode of transmission.
  • Adenovirus Infections: Adenoviruses can cause a wide range of symptoms, including fever, sore throat, cough, and conjunctivitis (pink eye), in addition to flu-like symptoms.

In addition to conditions that pass from person to person normally, there are also sexually transmitted diseases that can mimic flu symptoms and often go unnoticed until they are farther along in their progression. The most common of these diseases are: 

  • Human Immunodeficiency Virus (HIV): Acute HIV infection can produce flu-like symptoms, including fever, fatigue, muscle and joint aches, sore throat, swollen lymph nodes, and rash. However, these symptoms usually occur within a few weeks of initial exposure to the virus.
  • Syphilis: Early stages of syphilis (primary and secondary) can lead to flu-like symptoms, such as fever, fatigue, headache, muscle aches, and a sore throat. It is important to note that syphilis can progress to more serious stages with different symptoms.

What is the most effective treatment for influenza?

It should be noted that most cases of the flu resolve on their own, meaning that a person’s own immune system is able to fight the virus off, with most feeling better within a week. (11) However, in the event that a doctor opts for flu treatment, the most common options include: 

  • Oseltamivir Phosphate (Tamiflu®)
  • Zanamivir (Relenza®)
  • Peramivir (Rapivab®)
  • Baloxavir Marboxil (Xofluza®)

Antiviral treatment is particularly recommended for individuals at higher risk of complications from the flu, including:

  • Children under the age of 2
  • Adults aged 65 and older
  • Pregnant individuals
  • Individuals with certain underlying medical conditions such as:
    • Asthma
    • Diabetes
    • Heart Disease
  • Residents of long-term care facilities
  • Healthcare workers

In addition to antiviral medications, supportive care is essential for managing flu symptoms. This includes getting plenty of rest, staying hydrated, and using over-the-counter medications to alleviate specific symptoms like fever, cough, and congestion. Non-prescription pain relievers, such as acetaminophen or ibuprofen, can help reduce fever and ease body aches.

What is the primary management of influenza?

  • Rest and Hydration: Adequate rest is crucial for the body to recover from the flu. Staying hydrated by drinking plenty of fluids, such as water, herbal teas, and clear broths, helps prevent dehydration caused by fever and sweating.
  • Pain relievers and fever reducers: Acetaminophen (Tylenol) or non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil, Motrin) can reduce fever and relieve body aches.
  • Cough and cold remedies: OTC cough syrups or lozenges can help with cough and congestion.
  • Decongestants: These can relieve nasal congestion.
  • Isolation and Hygiene: To prevent the spread of the virus to others, individuals with the flu should:
    • Stay home until at least 24 hours after their fever is gone (without the use of fever-reducing medications).
    • Practice good respiratory hygiene, including covering their mouth and nose with a tissue or their elbow when coughing or sneezing.
    • Wash hands frequently with soap and water for at least 20 seconds.
  • Symptom Monitoring: Keep an eye on your symptoms and seek medical attention if they worsen or if you experience severe symptoms such as difficulty breathing, chest pain, confusion, or persistent high fever.
  • Preventive Measures: Encourage good hygiene practices, like regular handwashing and avoiding close contact with sick individuals, to reduce the risk of contracting or spreading the flu.

How do I get my strength back after the flu?

For some, the flu will take its toll on the body, with the resources that would normally be used for daily activities having been used to fight off the virus. In normal situations, the lasting effects of the flu that reduce results from physical activity are temporary. In the event that a person is weakened from the flu, some of the best ways to recover include: 

  • Rest: Adequate rest is crucial during the recovery process. Your body needs time to heal, and getting enough sleep will help your immune system work effectively. Aim for 7-9 hours of quality sleep each night, and consider taking short naps during the day if needed.
  • Hydration: Continue to drink plenty of fluids, even after your flu symptoms have improved. Staying hydrated helps your body recover and replace fluids lost through fever, sweating, and congestion. Water, herbal teas, and clear broths are good choices.
  • Nutrition: Eating a well-balanced diet is essential for recovery. Focus on foods that provide the nutrients your body needs to heal and regain strength. These may include:
    • Lean proteins like chicken, turkey, fish, and tofu for muscle repair.
    • Fruits and vegetables rich in vitamins and antioxidants to support your immune system.
    • Whole grains for energy and fiber.
    • Soups and broths for hydration and nourishment.
  • Gradual Physical Activity: After the flu, it's important to reintroduce physical activity slowly. Start with gentle activities like short walks or gentle stretching exercises. Avoid strenuous exercise until you feel significantly better. Consult your healthcare provider if you're unsure about when to resume your regular exercise routine.

How long should you be off work with the flu?

The duration of time you should be off work due to the flu can vary depending on the severity of your symptoms and your job responsibilities. Typically, it's recommended to stay home for at least 24 hours after your fever has subsided without the use of fever-reducing medications. In many cases, people with the flu may need to take 3 to 7 days off work to fully recover and prevent spreading the virus to coworkers. However, if you have severe symptoms or are in a high-risk group, a longer absence may be necessary, and it's essential to follow your healthcare provider's advice. (11) Those needing a doctor’s note for school or work can get one through Call-On-Doc today!

How do I know when the flu is gone?

You can generally tell when the flu is gone by monitoring the resolution of its symptoms. Common flu symptoms like fever, cough, body aches, and fatigue should noticeably improve or disappear altogether. Once you no longer experience these symptoms and your energy levels return to normal, it's a good indicator that your body has successfully fought off the virus. However, it's essential to note that some symptoms might linger for a few more days or even weeks, like a persistent cough or fatigue. If your symptoms persist or worsen, it's advisable to consult a healthcare professional for further guidance and evaluation to ensure there are no complications or secondary infections. 

Prevention: What is the best way to prevent influenza?

The best way to prevent the flu is through a combination of vaccination and good hygiene practices. Here are the key measures to help prevent the flu:

  • Flu Vaccination or Shot: Getting an annual flu vaccine is the most effective way to prevent the flu. The vaccine helps your immune system recognize and fight the influenza virus. It's recommended for everyone aged 6 months and older, especially for individuals at higher risk of complications, such as young children, the elderly, pregnant women, and those with certain medical conditions.
  • Hand Hygiene: Wash your hands frequently with soap and water for at least 20 seconds, especially after coughing, sneezing, using the restroom, and before eating. If soap and water are not available, use an alcohol-based hand sanitizer with at least 60% alcohol.
  • Respiratory Hygiene: Cover your mouth and nose with a tissue or your elbow when you cough or sneeze to prevent the spread of respiratory droplets containing the virus. Dispose of used tissues immediately and wash your hands afterward.
  • Avoid Close Contact: Try to avoid close contact with individuals who are sick with the flu. If you are sick, stay home from work or school to prevent spreading the virus to others.
  • Clean and Disinfect: Regularly clean and disinfect frequently touched surfaces and objects in your home and workplace, such as doorknobs, light switches, and computer keyboards.
  • Boost Your Immune System: Maintain a healthy lifestyle with a balanced diet, regular exercise, adequate sleep, and stress management to support your immune system's ability to fight off infections.
  • Avoid Touching Your Face: Avoid touching your eyes, nose, and mouth with unwashed hands, as this can introduce the virus into your body.
  • Use Face Masks: In situations where flu activity is high or during a flu outbreak, wearing a face mask, especially in crowded or indoor settings, can reduce the risk of transmission. It's essential to wear masks correctly, covering both your nose and mouth.
  • Stay Informed: Keep up with public health recommendations and guidelines related to flu prevention and vaccination, especially during flu season.

The flu is a highly contagious and aggressive disease that passes through our society yearly but isn’t something that leaves most patients with lasting symptoms or complications. However, that does not mean you should ignore such symptoms when they start to affect you. Get same-day treatment to start recovering faster with prescriptions sent to your pharmacy in 1-2 hours with Call-On-Doc, or select a priority visit and get your medication in less than 30 minutes!


  1. Fujimura, Sara F. “Purple Death: The Great Flu of 1918 - PAHO/WHO.” Pan American Health Organization, Perspectives in Health, https://www.paho.org/en/who-we-are/history-paho/purple-death-great-flu-1918.
  2. Gervais, Jessica B., and John Bulger. “Flu Statistics In 2023.” Forbes, Forbes Health, 26 January 2023, https://www.forbes.com/health/body/flu-statistics.
  3. “How Flu Spreads - How Flu Spreads.” CDC, https://www.cdc.gov/flu/about/disease/spread.htm.
  4. “Key Facts About Influenza (Flu).” CDC, https://www.cdc.gov/flu/about/keyfacts.htm.
  5. “Types of Influenza Viruses - Types of Influenza Viruses.” CDC, 30 March 2023, https://www.cdc.gov/flu/about/viruses/types.htm.
  6. LeBrun, Nancy, and Sameena Zahoor. “Flu A vs. Flu B: Symptoms, Causes, Treatment Options.” Verywell Health, 12 January 2023, https://www.verywellhealth.com/flu-a-vs-flu-b-7090660.
  7. “Upper Respiratory Infection: Symptoms, Contagious, Treatment.” Cleveland Clinic, 25 May 2021, https://my.clevelandclinic.org/health/articles/4022-upper-respiratory-infection.
  8. “COVID-19 vs. flu: Similarities and differences.” Mayo Clinic, https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/coronavirus-vs-flu/art-20490339.
  9. “Diagnosing Flu.” CDC, https://www.cdc.gov/flu/symptoms/testing.htm.
  10. “Flu Season - When Is Flu Season.” CDC, https://www.cdc.gov/flu/about/season/index.html.
  11. “When to Get Medical Help for Flu Symptoms - MN Dept. of Health.” Minnesota Department of Health, 26 October 2022, https://www.health.state.mn.us/diseases/flu/basics/flumedhelp.html.

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Wayne C. Hahne,

English graduate and Call-On-Doc’s medical resource guide, Wayne C. Hahne is an experienced and passionate medical education content expert. Through diligent research, provider interviews and utilizing the industry's leading resources for wellness information, it is Mr. Hahne’s personal mission to educate the general public on medical conditions with in-depth and easy-to-understand written guides.

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