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The Epidemiology of Influenza

Updated on February 24, 2017


According to the Centers for Disease Control and Prevention (CDC) (2016), the virus commonly known as influenza or “the flu” is actually several different strains that attack the upper respiratory system in humans, and that often use animals as carriers. The virus mutates rapidly enough that new vaccines for it must be produced each year, since it is technically not the same strain of virus as it was in previous years. The infection rates of the virus surge during the colder months, reaching its peak in winter. This period of elevated infection is known as the flu season, and over a quarter million people die annually during this time. Through preventative care and campaigns to promote vaccination, public health nurses can severely limit the effects of the influenza virus each year (Graham-Rowe, 2011).

Description of the Disease

Influenza causes fever, cough, sore throat, nasal congestion, muscle pain, headaches, and fatigue. Gastrointestinal distress is also known to occur should the virus spread to the stomach. According to Banning (2013), the flu is no longer infectious after five to seven days. However, the symptoms of the disease may persist in some form for up to two weeks prior to onset. Influenza is spread by airborne particles of moisture that are expelled from an infected individual when they cough, sneeze, or simply breathe. When another person inhales these particles, the risk of infection severely increases. For this reason, people who are not inoculated against the virus are encouraged to wear facial masks when exposed to infected individuals. (CDC, 2016).

According to the Banning (2013), influenza can cause serious complications in the lower respiratory system such as bronchitis and pneumonia. In some severe cases, neurological conditions can develop, such as cerebral edema and Guillain-Barre syndrome. Outside of neurological involvement, which is rare, the virus usually kills by way of excessive compromising of the lower respiratory system which impedes the body’s ability to receive oxygen, thus weakening the body further and creating a cycle in which the immune system cannot fight off the infection.

According to the CDC (2016), preventative medicine is the single most effective way to combat influenza. The vaccine for influenza is updated each year and is distributed to the populace. Extensive public health campaigns are funded to educate people on the need to receive a vaccine, and charitable organizations attempt to make them available to indigent communities. In addition to protecting those who are inoculated, widespread administration of the vaccine removes these people as potential hosts for the virus and impedes its spread. Secondary care for influenza is possible with the use of antiviral medication, though these are not a cure and are not as effective as prevention (Banning, 2013).

According to Graham-Rowe (2011), the rate of influenza-related death has increased significantly over the past decade due to the emergence of two particular strains: H5N1 or “bird flu” and H1N1 or “swine flu. While bird flu is more lethal but less contagious, swine flu is more contagious but less lethal. Together, these two strains have increased the morbidity and mortality rates of influenza globally. According to the CDC (2016), during the 2014-2015 influenza season, approximately 33% of patients who had respiratory testing done were positive for some strain of the influenza virus.

Determinants of Health

According to Maurer and Smith (2009), the epidemiological triangle comprises four parts: host, environment, agent, and time. Humans are the host for influenza as they are the animal capable of full blown infection. The weaker a human’s immune system, the more suitable a host for the virus. Immunocompromised patients are at extremely high risk with regards to influenza. (CDC, 2016).

One important environmental factor discussed by Graham-Rowe (2011) is the animal carriers fo the disease. Strains of the illness such as H1N1 (swine flu) and H5N1 (bird flu) can have reservoirs in these respective animals. Any human exposed to these animals due to geography or livelihood is at a higher risk of infection. Other environmental factors exist such as exposure to other hosts. A health care worker is in one of the most exposed situations, and has a poor environmental determinant of health as compared to someone who has very little risk of exposure (CDC, 2016).

The agent of the virus is the moisture particles by which the virus is transmitted between people. Very simple hygienic practices can affect this determinant of health, such as covering one’s mouth during sneezing or coughing and hand washing. One’s education about disease prevention and the adherence to such protocol is an important determining factor in influenza risk (CDC, 2016).

The final determinant of health is the incubation and symptomatic period for the disease. As mentioned earlier, the virus has stopped being infectious after 5 to 7 days within a host, though the host may continue showing symptoms for up to two weeks. This element of time is the final piece of the epidemiological triangle (time), and it is represented by the center of the triangle (Banning, 2013; Maurer & Smith, 2009).

Role of the Community Health Nurse

According to Maurer & Smith (2009), investigation and reporting on rates and instances of communicable diseases is one of the primary roles of a community health nurse. It is community health nurses that gather statistics on diseases such as influenza and report their findings to the CDC. In this way, a community health nurse’s main role in addressing influenza is in information collection for the purpose of creating a more educated and prepared populace. The information gathered by them allows for accurate risk assessment and to track the progress of interventions. A vaccine’s effectiveness is rated by this collected data, and the following years’ vaccine is produced while referencing this same data. Without research and reporting, the scientists who produce the vaccine would essentially be operating blindly.

In a local sense, community health nurses can design advertising campaigns and community workshops to ensure that people understand the risks of influenza and the benefits of receiving the vaccine. The organization of charitable funding, policy reform in schools, and direct interaction with the public all fall under the purview of the community health nurse in addressing influenza (Maurer & Smith, 2009).

The World Health Organization (WHO) disseminates literature on influenza prevention, helps advocate for and organize funding for the vaccine to reach impoverished communities around the world, and has an integral position in the fight against influenza globally. Since the early 1970s, WHO has been involved in researching influenza and its ever-changing strains. Since that time, WHO has provided the companies which produce the vaccine the information necessary to determine the composition of the vaccine and which strains it should target.


The main tool the medical system has in combating influenza is education, both of the populace and of the researchers studying the disease. Due to the ever-changing nature of the multiple strains of the virus, influenza cannot be “cured” and instead a battle is fought each year to minimize its effect on the population. Community health nurses play an important role in both the data collection and dissemination of information regarding influenza for the purposes of effective preventative care.


Banning, M. (2013). Influenza: Incidence, symptoms and treatment. British Journal of Nursing, 14(22), 1192-1197. Retrieved June 30, 2016, from

Centers for Disease Control and Prevention (2016). Seasonal influenza. Retrieved June 30, 2016 from

Graham-Rowe, D. (2011). Epidemiology: Racing against the flu. Nature,480(7376).

Maurer, F. A., & Smith, C. M. (2009). Community/public health nursing practice: Health for families and populations. St. Louis, MO: Elsevier/Saunders.

World Health Organization (2016). Influenza vaccine viruses and reagents. Retrieved June 30, 2016 from


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      Louise Powles 2 months ago from Great Yarmouth

      I had the flu once and it was awful. Thanks for the information, it's been interesting reading about this.

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