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Epidemiology: Influenza

Epidemiology: Influenza

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Causes of Influenza

Influenza is a viral disease that occurs in many strains, and it affects both human and animals. It is a communicable disease, and it is highly transmitted from one person to another or from animals to human beings. Two types of viruses cause influenza, type A and type B. The two types of virus that cause influenza can change into different forms upon mutation in human cells. Influenza virus type A has sixteen subtypes with hemagglutinin (HA) surface and nine subtypes with neuraminidase (A) surface (WHO, 2011). Type B virus does not have subtypes

Symptoms of Influenza

One a person becomes infected with influenza virus; the symptoms can be noted one or two days after the infection. Newborns and infants may show some symptoms such as dehydration, difficulties in breathing, reduced feeding, and low-grade temperature. Adults may experience fever, headache, sore throat, nausea, diarrhea, muscles aches, sneezing and abdominal cramps (WHO, 2011). During this period, the affected people are highly infectious, and they can infect a large number of people.

Modes of transmission

Influenza is transmitted mainly through the air. The virus that causes Influenza is carried by droplets when one coughs, sneezes or puts the mouth on an object. Also, people who get close enough to the patients who are affected by influenza can inhale the virus or when they come in close contact with the object that maybe containing the virus such as hands of people who are infected with influenza virus then touching their mouth, nose or even eyes.


The major complication of influenza is pneumonia. The secondary bacterial pneumonia is the most common while primary bacterial pneumonia is rare though it has highly fatal rate. Children especially those taking aspirin and who are affected by type B virus of influenza experiences the complication of Reye syndrome (Grohskopf, Tokars & Tom, 2015). Children with this complication indicate symptoms such as vomiting, confusion and in severe cases the go into a coma as it causes the brain to swell. Inflammation of the heart, a condition known as myocarditis is also another complication of influenza. Chronic pulmonary diseases usually accompany this and worsening of chronic bronchitis.

Influenza Treatment

Influenza (Flu) is treated using the antiviral drugs that fight influenza virus from the body. For the safety of the patients, once an outbreak of influenza has been reported, it becomes their responsibility to get a vaccination for prevention from its attacks. The antiviral drugs help in preventing serious flu complications especially for people with chronic health conditions such as diabetes and asthma. Some of the antiviral drugs that are recommended for treatment of flu include peramivir (Rapivab), zanamivir (relenza) and oseltamivir (Tamilflu) (CDCP, 2015). The medication have been approved by the Food and Drugs Association (FDA). The Center for Disease Control and Prevention (CDCP) also recommends these drugs. The drugs may, however, have some side effects such as dizziness, nausea, headache and some behavioral side effects.

Demographics of interest

Since the 19th century, five influenza pandemics have been experienced. The attacks have been shown to involve all age groups, and the mortality rate has markedly increased. In 2009, flu of type A (H1N1) outbreak occurred in North America and later it had spread to most parts of the world. This pandemic had rampant effects as CDC reported in 2011 that more than 60 million Americans became ill, 270,000 were hospitalized and 12500 died (Grohskopf, Jerome, 2015). The number of deaths that occurred among the hospitalized patients was mostly among young people not older than 65 ranging up to 90% of the death cases (Grohskopf, Jerome, 2015). The greatest impacts were found in morbidity with high attacks commonly in adults with respiratory complications.


Determinants of health

Determinants of health are factors that have impacts on people’s health such as genetics, the environment in which they live, financial income, relationships with friends and family and level of education. World Health Organization (WHO) groups these factors into three categories

  • The Physical Environment – People who live in an environment where there is clean air, clean water, healthy working environment and safe houses are associated with good health. Also, the employment and working conditions contribute to determining the health conditions of human being (WHO, 2015). People in employment and especially those who can control their working conditions are healthier than the unemployed once. People who live in places where they can access health facilities easily are also healthier than those who live in remote areas that have poor roads for access to health facilities.
  • Personal characteristic and individual behaviors – The genes that people inherit from their parents play a crucial role in the determination of healthiness, lifespan and probability of developing certain diseases (WHO, 2015). Also, individual behaviors such as smoking, being active, eating balanced diet food, drinking of alcoholic substances and how people deal with stress and life challenges also determines their health.
  • Social and economic environment – People who have greater access to support from their friends, families and community are linked with good health conditions. Beliefs, traditions, customs and cultures also affect the health of the community. People with higher income and high social status are associated with good health. Poor people in the society experiences challenging health conditions.

These factors mentioned above contribute significantly to the development and the spread of Influenza. There is a higher likelihood that people who live in an environment where there are many other residents congested together develops influenza. Aged people and people with special conditions in the society such as pregnant women, infants, and young children have a higher likelihood to develop influenza (WHO, 2015). Also, the environment in which people work for instance health workers are likely to come in contact with patients suffering from influenza thus their chances of developing influenza is high. Also, health conditions such as diabetes, asthma, and chronic heart diseases increases chances of developing chronic influenza.

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Epidemiologic Triangle

An epidemiological triangle is a scientific model that helps in studying and understanding related health problems. It has three vertices namely:

  • Host – a microbe that causes the disease
  • Agent – an organism harboring the disease “who of the triangle.”
  • Environment – factors that contribute to transmission of the disease.

In the case of influenza disease, the Agent here is a virus. The hosts are both a human being and the animals. They are affected by the virus, and also they harbor it for transmission. The environments that favor the outbreak and transmission of influenza are congested places, contacts that cause contacts with mouth and mouth fluids and droplets from coughing and sneezing.

Host Factors

  • Human mobility – This factor is significance especially in the spread of influenza. When infected people are more mobile, they tend to spread the disease more.
  • Immunity – Immunity against influenza depends on the presence of antibodies.

After the infection with influenza, secondary antibodies develop in the respiratory tract that mainly consists of lgG (Gujarati, 2015). For this to be possible, the antibodies titer should be high in the blood so that they can neutralize the virus and modify the infection. Age and sex – Influenza has been found to attack people of both gender and across all the ages. Children, however, form the most vulnerable group for this disease most especially infants under the age of two years. Also, old people are more likely to be attacked as compared to young adults.

Agent factors

Flu is caused by two types of viruses: Type A and type B. The two types of viruses have different surface antigens. Type A has Hemaglutinin's (H) while type B has Neuraminidase (N) antigens (Gujarati, 2015). Influenza infection is initiated by the H antigen, and the virus is released from the infected cell by antigen (N). The reservoir of infection – Animals and birds form the major reservoir of influenza virus. Flu Viruses are also able to recombine and form new strains in animals.

  • Period infectivity – Influenza virus is usually present in the nasopharynx 1 or 2 days before and after the appearance of the symptoms.
  • Source of infection – The sections of the respiratory track are usually infective, and they contribute significantly to the transmission of influenza.

Environmental factors

  • Season – Most incidences of influenza outbreak are seasonal striking mostly during winter in the northern hemisphere. It has however been seen to occur in summer in India (Gujarati, 2015).
  • Overcrowding – Overcrowding escalates the rate at which influenza is transmitted. In places where there are large number of people in closed rooms such as churches and schools, the transmission rate is high.


The role of the community health nurse

Community health nurses investigate the outbreak of influenza to determine the size, the stage, and the geographical spread of the disease (WHO, 2011). They also identify the case load. This is achieved by monitoring the influenza strain through public health laboratories and the Melbourne-based WHO Collaborating Center for Reference and Research on Influenza. Once confirmed, the severity of influenza outbreak is monitored through hospitalization data, ICU data and deaths. The regions that are at high risk are reported through passive reporting from those areas. Other relevant information that the community health nurses collect is number of trained Care Health Workers (CHWs), availability of various channels of health education, coverage of the region with appropriate information and the availability of medication equipment and stock (WHO, 2011). After the data has been corrected for ICU data, hospitalization cases, and deaths, and from the affected regions, the data is analyzed and entered into jurisdiction notification databases and then transferred to the National Notifiable Diseases and Surveillance System (NNDSS). The Community Health Nurses also report the total number of ILI cases, deaths and Acute Respiratory Infection (ARI). For a single notification, follow-up activities are not necessary. Instead, the community health nurses focus on outbreaks in high-risk areas.


National Agency that addresses Influenza

National Center for Immunization and Respiratory Diseases (NCIRD) is a national agency works towards improving Influenza control and prevention. The organization focuses on enhancing pandemic preparedness and response by building surveillance and response capacity, monitoring and assessing influenza viruses and illness and improving vaccines and other interventions related to influenza (NCIRD, 2015).


CDCP (2015). Why CDC Recommends Influenza Antiviral Drugs. Center for Disease Control and Prevention. Retrieved from http://www.cdc.gov/media/haveyouheard/hyh-antiviraldrugs.html on 22nd May 2015 Drs. Lisa Grohskopf, Jerome Tokars, Tom. (2015). Influenza. Centers for Disease Control and Prevention Epidemiology and Prevention of Vaccine-Preventable Diseases, 13th Edition Gujarati, M. (2015). Causative Factors of Influenza. Aarogya Network. Retrieved on 22nd May 2015 from: http://www.aarogya.com/conditions-and-diseases/influenza/causative-factors-of-influenza.html (NCIRD). (2015). Influenza Division. National Center for Immunization and Respiratory Diseases (NCIRD). Retrieved on 23rd May 2015 from http://www.cdc.gov/ncird/flu.html WHO. (2011). Community case management during an influenza outbreak. Trainer’s Guide a Training Package for Community Health Workers. WHO. (2015). The determinants of health. Health Impact Assessment (HIA). Retrieved from http://www.who.int/hia/evidence/doh/en/ on 22nd May 2015.

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