Definition
A.Influenza is a common, acute, viral infection that is a self-limiting, febrile illness of the respiratory tract. Illness is spread person to person, primarily by respiratory secretions that can be spread from infected persons through sneezing, coughing, talking, and self-inoculation of secretions through direct contact routes. Influenza is one of the top 10 causes of death in the United States when it occurs with pneumonia.
Incidence
A.Epidemics occur yearly, primarily in the winter months, in both the northern and southern hemispheres. Travelers should be reminded that the flu season is different by hemisphere and can occur on cruise ships. Attack rates may be as high as 10% to 20% of the population. Mortality is highest in the geriatric population older than 65 years of age, except during pandemics when 50% of influenza deaths occur in individuals younger than 65 years of age. Extraordinarily high attacks have occurred in the institutionalized and crowded populations.
Pathogenesis
A.Influenza A and B are viruses that have the ability to undergo periodic antigenic changes of their envelope glycoproteins, the hemagglutinin and neuraminidase. Among influenza A viruses that infect humans, there are three major subtypes of hemagglutinins (H1, H2, and H3) and two subtypes of neuraminidases (N1 and N2). Influenza A outbreaks typically start abruptly, peak over 2 to 3 weeks, and last approximately 2 to 3 months. H1N1 (swine flu) is an influenza A virus.
B.The avian flu was the N5N1 and H7N7 viral infection associated with recent exposure to dead or ill poultry. Following exposure, the incubation period for human H5N1 infection was 7 days or less. Clusters of human-to-human transmission of avian flu had a typical incubation period of 3 to 5 days.
C.Influenza B outbreaks are generally less extensive and less severe. Outbreaks associated with the B virus have been reported in schools, military camps, nursing homes, and cruise ships.
D.Haemophilus influenzae is a Gram-negative coccobacillus. H. influenzae is an invasive bacterial disease that can cause meningitis, otitis media, sinusitis, epiglottitis, septic arthritis, occult febrile bacteremia, cellulitis, pneumonia, and empyema; occasionally, this virulent organism causes neonatal meningitis.
E.The incubation period for H. influenzae is from between 18 and 72 hours to 5 days after exposure. The exact period of communicability for H. influenzae is unknown, but it may be for as long as the organism is present in the upper respiratory tract.
Predisposing Factors
A.The primary mode of spread is via exposure to viral strain respiratory secretions from respiratory droplets (coughing or sneezing) and direct contact of contaminated surfaces:
1.Adults:
a.Aged older than 65 years (dependent on the viral strain).
b.Pregnancy.
c.High-exposure jobs: Teachers, healthcare workers, police, and firefighters.
d.Recent illnesses or state that has lowered resistance (stress, excessive fatigue, poor nutrition).
e.Immunosuppression from drugs, illness, or chronic illness (transplant recipients, lung disease, heart disease).
f.Crowded living conditions, including military camps and institutions such as nursing homes.
g.Travel in endemic areas.
h.Avian flu: Exposure to dead or ill poultry.
Common Complaints
A.Clinical manifestations of influenza depend on age and previous experience with the influenza virus.
B.Rapid-onset respiratory illness is the most common complaint.
C.Abrupt onset of fever and/or chills.
D.Joint pain.
E.Headache.
F.Conjunctivitis (avian flu).
Other Signs and Symptoms
A.Upper respiratory congestion (watery eyes, clear nasal drainage, headache, sore throat, and hoarseness).
B.Malaise or fatigue.
C.Anorexia.
D.Swollen lymph nodes.
E.Nonproductive cough (persisting for weeks).
F.Muscle aches.
G.Gastrointestinal symptoms.
H.Febrile seizures.
I.Otitis media.
Subjective Data
A.Review the onset, course, and duration of symptoms, especially myalgia and malaise.
B.Query the patient if they have had a flu shot and when the last flu vaccination was received.
C.Review symptoms of other family members or coworkers who are also ill.
D.Review for recent travel location and use of cruise ships or planes.
E.Evaluate living conditions for exposure risks.
F.Is the patient a smoker?
G.Review all medications, including over-the-counter (OTC) and herbal products. Has the patient taken any medications for the symptoms?
H.Does the patient have a history of asthma or chronic obstructive pulmonary disease (COPD)?
I.Is the patient immunocompromised (i.e., has HIV, is a transplant recipient, is on chemotherapy)?
J.What other medical comorbidities, such as diabetes, does the patient have?
K.In patients 65 and older, is illness associated with new onset confusion, which may indicate sepsis?
Physical Examination
A.Check temperature, pulse, respirations, and blood pressure (BP).
B.Inspect:
1.Observe overall appearance for pallor and for any respiratory distress.
2.Assess hydration status of mucous membranes.
3.Conduct an eye, ear, nose, and throat exam.
4.Assess skin for rashes, petechiae, and turgor.
C.Auscultate:
1.Auscultate the lung fields, observing for wheezing and crackles.
2.Auscultate the heart.
D.Palpate: Palpate the neck and lymph nodes: preauricular, posterior auricular, submental and sublingual, anterior cervical chain, and supraclavicular nodes.
E.Neurologic exam:
1.Assess level of consciousness (LOC).
2.Assess for nuchal rigidity.
3.Assess for meningeal signs:
a.Signs of meningeal irritation include nuchal rigidity.
b.Positive Brudzinski’s and Kernig’s signs (refer to Figures 12.1 and 12.2):
i.Brudzinski’s sign: Place the patient supine and flex the head upward. Resulting flexion of both hips, knees, and ankles with neck flexion indicates meningeal irritation.
FIGURE 12.1Brudzinski’s sign.
ii.Kernig’s sign: Place the patient supine. Keeping one leg straight, flex the other hip and knee to a bent knee to form a 90° angle. Slowly extend the lower leg. This places a stretch on the meninges, resulting in pain and spasm for the hamstring muscle. Resistance to further extension can be felt.
FIGURE 12.2Kernig’s sign.
Diagnostic Tests
A.Usually none is required. However, if the patient appears ill, consider the following:
1.White blood cell (WBC) and complete blood count (CBC).
2.Viral RNA cultures: Obtain during the first 72 hours of illness because the quality of virus shed subsequently decreases rapidly. There is some evidence that a throat sampling yields an improved specimen. Nasopharyngeal secretions obtained by swab or aspirate should be placed in an appropriate transport medium for culture.
3.Rapid antigen test (usually less sensitive in the detection of influenza A than the polymerase chain reaction [PCR]; a negative rapid diagnostic test should be confirmed with a viral culture or other means).
4.Monospot test: Monospot test is negative with the flu and positive with mononucleosis.
5.Chest radiograph (CXR; only if pneumonia suspected).
6.Sputum culture (complications only).
7.Lumbar puncture (complications only).
8.Rapid plasma reagin (RPR) test (for high-risk HIV factors): Negative RPR to rule out syphilis.
9.PCR assay (it can differentiate between influenza subtypes and offers high sensitivity and specificity but is not readily available for clinical use).
Differential Diagnoses
A.Influenza:
1.Influenza A.
2.Influenza B.
3.Avian flu (H5N1).
4.H1N1 (swine flu).
B.Pneumonia.
C.Bronchitis.
D.Mononucleosis.
E.Early HIV.
F.Severe acute respiratory syndrome (SARS).
G.Meningitis.
Plan
A.General interventions:
1.Management is usually treatment of symptoms.
2.Encourage flu vaccine for patients in susceptible populations prior to flu season.
3.Patients should expect to have a persistent cough and malaise after initial acute phase.
B. 
See Section III: Patient Teaching Guide Influenza (Flu).
C.Pharmaceutical therapy:
Influenza can alter the metabolism of certain medications, especially theophylline, possibly resulting in the development of toxicity from high serum concentrations.
1.Acetaminophen (Tylenol) as needed for fever.
2.Nonsteroidal anti-inflammatory drugs (NSAIDs) as needed for body aches.
3.Amantadine and rimantadine (class of medications known as adamantanes) are not recommended for antiviral treatment or chemoprophylaxis of currently circulating influenza A virus strains.
4.Antivirals started within the first 48 hours confer the greatest benefit. Antiviral therapy recommendations vary by type of influenza, age group, renal function, and risk factor. To prescribe the most current antiviral therapy, refer to the Centers for Disease Control and Prevention (CDC) website for the most up-to-date recommendations: www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm.
5.The recommended duration of treatment is 5 days. Longer treatment regimens may be necessary in persons with immunosuppression for hospitalized patients.
6.Zanamivir (Relenza):
a.Not recommended for persons with underlying airway disease, including asthma or COPD.
b.Zanamivir is for uncomplicated acute illness due to influenza A or B in adults who have been symptomatic for no more than 2 days.
c.See Table 12.2 for the recommended dosage and schedule of influenza antivirals for treatment and chemoprophylaxis.