COMMENTARY

4 Influenza Myths Debunked

Helen Keipp B. Talbot, MD, MPH; Thomas R. Talbot, MD, MPH

Disclosures

March 10, 2017

Common Influenza Misconceptions

Each year, as the influenza season hits its stride, clinicians are faced with common misconceptions on the part of patients about this important and serious infection. Here, we address four of these common misconceptions about influenza.

Myth 1: Influenza Is a Harmless Illness

The notion that influenza infection is mild and "not a problem" is pretty pervasive. Part of the challenge in tackling this belief is that the term "flu" is often used to describe many different illnesses, from the common cold and gastroenteritis to actual laboratory-confirmed influenza infection. Unfortunately, widespread use of the term "flu" has created the misconception among patients that influenza is not a serious illness. This is compounded by the reality that for some individuals, influenza may not cause the classic syndrome of fevers, myalgias, fatigue, chills, and lethargy.

The severity of influenza can range from mild illness to death. Disease severity depends on the circulating influenza strain as well as individual patient factors, such as comorbid conditions, age, previous influenza exposure, vaccination status, and overall health.

The severity of influenza can range from mild illness to death.

Epidemiologic data show that influenza infection is not harmless. Influenza is associated with 23,607 deaths[1] and 226,054 hospitalizations[2] each year. Even if not hospitalized, an influenza-infected person can subsequently develop such serious complications as myocardial infarction or stroke.[3] Influenza also may present with atypical symptoms, particularly in patients at the extremes of age. Older adults, for instance, often present without fever, likely owing to immune senescence.

In healthy adults, infection with influenza can be asymptomatic or produce only mild symptoms, such as rhinorrhea or a slight cough. Influenza can cause significant disease in children, as seen by an average annual hospitalization rate of 0.9 per 1000 infected children and an estimated burden of 50-95 outpatient clinic visits and 6-27 emergency department visits per 1000 children.[4]

Myth 2: Influenza Is Contagious Only if the Infected Person Is Symptomatic

Influenza is primarily transmitted from person to person. The viruses are spread by large droplets that develop when the infected person coughs, sneezes, or talks. These droplets can land in the mouth or nose of those nearby and be inhaled into the lungs. Transmission also occurs through contact with the environment, fomites, or the mucous membranes of an infected person.

Although transmission is most likely when the infected person has symptoms, data suggest a role for asymptomatic infection in the spread of influenza. The influenza virus is detectable in the upper airway and nasopharynx of influenza-infected persons for several days before symptom onset.

A study[5] from Hong Kong followed a cohort of 824 households from 2008 to 2014. The researchers identified 224 cases of secondary influenza that developed in the home and examined the relationship between symptoms and viral shedding (as detected on nasal and throat swabs). Viral shedding without symptoms varied somewhat by influenza strain. Shedding was detected before the onset of respiratory symptoms in influenza A–infected persons but peaked during the first 2 days of clinical illness, whereas influenza B shedding peaked up to 2 days before symptom onset. This suggests the potential for influenza virus transmission in the presymptomatic phase of the illness.

[E]ven healthcare workers with classic influenza-like illness and fever... typically continue to work.

Influenza is clearly detectable in the nasopharynx of asymptomatic persons, but there is some debate as to the role this plays in transmission (ie, is there viral shedding and transmission outside of the nasopharynx if no symptoms are present?). One pragmatic nuance of this debate, however, is that even if an asymptomatic person doesn't transmit the virus to others, the development of symptoms—even mild symptoms—can facilitate spread. For example, the asymptomatic person with detectable virus in the upper airway, who develops mild rhinorrhea, can unknowingly spread the virus to others.

Some argue that once symptoms develop, the infected person will avoid contact with high-risk colleagues by leaving work or staying home, but that simply does not happen. Data consistently show that even healthcare workers with classic influenza-like illness and fever (a far more severe illness than mild upper respiratory symptoms) typically continue to work.[6,7,8,9] To expect that those with mild respiratory symptoms will remove themselves from work or close household contact is unrealistic.

Myth 3: I Have Never Had the Flu, so I Don't Need a Flu Shot

This common argument against vaccination has a few variations: "I have a healthy diet/I exercise/I wash my hands. I never get the flu shot, and I've never been sick with the flu."

Just because someone has never had influenza doesn't mean that person won't become infected in the future. Even healthy people can become infected and critically ill with influenza, as evidenced by the morbidity rates during the H1N1 influenza A pandemic in 2009. Furthermore, even without symptoms, an infected person can serve as a vector and spread influenza to others.

When trying to counter the misconception about the need for a flu shot, the use of seat belts is a good analogy. Many people who don't wear seatbelts have never had an automobile accident; however, it is clearly safer to wear seat belts to reduce the risk for injury and death in the event of an accident.

Acceptance of the influenza vaccine can be influenced by how physicians discuss annual influenza vaccination with their patients. Often patients are asked, "Would you like a flu shot?" Compare this with how other important medications are discussed. We don't ask patients with diabetes whether they would like to take insulin; instead, we recommend insulin as an important medical treatment. Similarly, we should not ask patients whether they want the influenza vaccine but strongly recommend annual influenza vaccination.

Myth 4: Nothing Can Be Done to Prevent Influenza

Many interventions, in fact, can reduce the chances of becoming infected with influenza. Adherence to infection prevention strategies, such as hand hygiene, cough etiquette, and respiratory hygiene, and avoiding others when ill, are all very important. Influenza vaccination is another important tool in the prevention of influenza.

The level of protection of the annual vaccine varies and is affected by such factors as the predominant circulating strain and the recipient's vaccination history and immune status. On average, the vaccine is 59% effective in adults aged 18-65 years[10] and 20%-44% effective in those aged 65 years or older.[11] Hence, protection is not optimal, but vaccination prevents illness and hospitalization in large numbers.

 
Influenza can be a severe, life-threatening illness.
 

Antiviral medications, including oseltamivir and inhaled zanamivir, can also be used for chemoprophylaxis. Rimantadine and amantadine are no longer recommended because of resistance that has developed in many circulating strains of influenza.

One of the most common uses of antivirals for prevention occurs in residential facilities to reduce transmission after a case of influenza has been identified. This approach also can be used in families, especially if family members with high-risk conditions are exposed to influenza.

Take-Home Messages for Clinicians

Influenza can be a severe, life-threatening illness. It can affect anyone but is especially dangerous in those with underlying conditions, pregnancy, or extremes of age. Influenza is readily transmissible, and transmission begins before symptoms manifest. Infected persons may have atypical symptoms or no symptoms at all.

Antivirals and vaccination are important but imperfect methods for prevention and should be combined with basic infection prevention methods to reduce the spread of this important disease.

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