Optimizing Barrier Protection During a
Pandemic Event Caused by Influenza A

Pathophysiology of Influenza Type A DEFINITION Influenza A is a rhinovirus commonly known as “the flu.” It originates from the orthomyxoviridae family, which attacks the respiratory tract. The name “influenza” originated in 15th century Italy from an epidemic attributed to “influence of the stars.” There are three distinct immunological types (A, B, C), based on nucleocapsid and matric proteins. Influenza A has numerous subtypes named for hemagglutinin and neuraminidase. Influenza B and C are milder forms that do not mutate as much as influenza A. Listed below are subtypes for influenza A identified to date: H3N2, H1N1, H1N2 (Common human) H5N1, H7N7, and H7N3 (Avian Influenza) These viruses have been associated with HPAI, and human infection with these viruses has ranged from mild (H7N3, H7N7) to severe and fatal disease (H7N7, H5N1). LPAI viruses have been documented, including very mild symptoms (e.g., conjunctivitis) to influenza-like illness. Examples of LPAI viruses that have infected humans include H7N7, H9N2, and H7N2.18 All pandemic occurrences of influenza have been caused by influenza A. Populations tend to have greater resistance to influenza B and C because they only undergo antigenic drift and are more similar to previous strains.19 In the general population, influenza has been recognized as a seasonal flu that is unimportant and uninteresting; it has been dismissed as a passing nuisance. It is complicated to obtain an accurate approximation of the infectivity of new virus strains. CLINICAL MANIFESTATION With influenza A, patients will develop symptoms of fever, sore throat, and muscle aches or eye infections. In extreme or fatal situations, severe respiratory distress and secondary pneumonia can occur. Under these circumstances, an increased heart rate, increased respiratory rate, high liver enzymes, shortness of breath, dyspnea, and cough would be present.20 Recently, atypical manifestations of diarrhea and CNS involvement21 have been observed. INCUBATION PERIOD Typically ranges from 1-4 days. The virus is first detected just before the onset of symptoms and is usually not detected after 5-10 days. There is also more prolonged shedding from children—a typically immunosupressed host—than normally healthy adults.22 CAUSE The influenza virus is composed of a lipoprotein envelope surrounding a core of genetic material of ribonucleic acid (RNA). The RNA contains all of the genes necessary for the virus to survive and reproduce in the cells of the host.23 DIAGNOSIS The rapid polymerase chain reaction (PCR) test is used to diagnose the flu. This test is found to be rapid and reliable.24 The following questions should be asked when a patient with a febrile respiratory illness is encountered: Have you been traveling or in contact with anyone who has been traveling within the last 10 days? Have you been in contact with or been around someone who has been in contact with any birds within the last 10 days (i.e., live poultry farm, live bird market, or anywhere that poultry is raised)?25 POST-EXPOSURE PROPHYLAXIS Available influenza antiviral agents are separated into two classes. The first class of products is the adamantane, which includes amantadine and rimantadine and works by preventing membrane fusion. These agents are active against influenza A viruses but not influenza B viruses. Reports of resistance to amantadine and rimantidine in humans infected by H5N1 (current strain of Avian influenza) have been described. The second class of products is the neuraminidase inhibitors, which includes zanamivir and oseltamivir. These products prevent release of intact viruses from infected cells. These agents are active against both influenza A and B viruses. Both antiviral medications oseltamivir and zanamivir are approved for treatment. The efficacy of these drugs during treatment of H5N1 virus infection is being investigated at this time.24 LONG-TERM EFFECTS In severe circumstances, or if left untreated, death could occur. The only reliable source to date is the last three pandemic occurrences. No other long-term effects have been reported. TREATMENT Many marketed influenza antiviral agents are available and approved by the U.S. Food and Drug Administration (FDA) for the treatment of influenza A. The neuraminidase inhibitors such as oseltamivir (Tamiflu) and zanamivir (Relenza)26, as well as M2 ion channel inhibitors such as rimantadine (Flumadine) and amantadine (Symmetrel), could all be used to treat this virus. Studies of the safety and efficacy of these products are ongoing. It is important to note that side effects can occur from these antivirals. These side effects present as headache, myalgia, diarrhea, and possibly an increase in liver enzymes.27 For additional information, please refer to the pharmaceutical compendium of the specific product. VACCINE It is recommended that the following people be vaccinated with inactivated influenza, since they are at an increased risk for complications; however, there is no available H5N1 vaccine at the time of this publication. Healthcare workers (the most important way to prevent the spread of influenza in a healthcare setting is for the patient and the healthcare worker to be vaccinated). People 50 years and older. Residents of nursing homes. People of all ages who have chronic medical conditions (including chronic disorders of the pulmonary and cardiovascular systems, asthma conditions, diabetes mellitus, renal dysfunction, hemoglobinopathies, or immunosuppression). Children and adolescents (aged 6 months to 18 years) who are receiving long-term aspirin therapy, as they may be at risk for experiencing Reye’s Syndrome following influenza infection. Pregnant women Children aged 6 months until their fifth birthday.28 TRANSMISSION Influenza A is transmitted via droplets, meaning person-to-person, direct contact, or through aerosol (sneezing, coughing, etc.).29 The Avian Flu can occur as a result of coming into contact with contaminated poultry or surfaces contaminated from a bird. Infected birds shed flu virus in their saliva, nasal secretions, and feces.30 This disease may also be contracted through an intermediate host, such as a pig. As a result, a new virus develops that may be able to infect humans and spread from person to person. This type of major change in the influenza A viruses is known as an antigenic shift.31 An antigenic shift is defined by a sudden shift in the antigenicity of a virus resulting from the recombination of the genomes of two viral strains. Antigenic shift is seen only with influenza A viruses.32 FACTS, STATISTICS, AND TRENDS Influenza is the single most vaccinepreventable disease.32 Approximately 5% to 20% of the population will get the flu each year.32 More than 200,000 people are hospitalized from flu complications.32 Because of the short incubation period and abrupt onset, it is very unpredictable where and when this disease could occur. The type of virulent strain, the susceptibility of the population it is affecting, how well the population was vaccinated, and how the vaccine is matched with the strain of influenza dictates the severity of the outbreak of influenza A. The bird vaccination exacerbated the pathogenicity of H5N1 to new strains of viruses. (It forced mutations at the H and N alleles, elevating the risk of its passing on to humans.) H5N1 has now spread to Russia and has infected poultry and tigers. According to 2003 data, only 36% of healthcare workers are actually immunized against influenza each year.34

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