Influenza resident survival guide

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mounika Reddy Vadiyala, M.B.B.S.[2]

Overview

Influenza, commonly known as the flu, is an infectious disease caused by the RNA virus called the influenza viruses A and B.

Causes

Common Causes

• Influenza A
• Influenza B

Complete Diagnostic Approach

Characterize the symptoms: ❑ Fever ❑ Abrupt onset ❑ Ranges from 37.8 to 40.0°C, but it can get as high as 41.1°C (106°F) ❑ Associated with chills ❑ Headache ❑ Cough ❑ Non-productive ❑ Myalgia ❑ Chills ❑ Rhinorrhea ❑ Nasal congestion ❑ Sore throat ❑ Fatigue ❑ Pleuritic chest pain ❑ Malaise Less common symptoms: ❑ Vomiting ❑ Diarrhoea ❑ Abdominal pain ❑ Loss of appetite ❑ Dizziness ❑ Weakness

Obtain a detailed history: ❑ Age ❑ List of medications Identify persons who are at high risk of complications from Influenza: ❑ Children aged younger than 2 years ❑ Adults aged 65 years and older ❑ Persons with the following comorbidities: ❑ Chronic pulmonary disorders (including asthma) ❑ Cardiovascular disorders(except hypertension alone) ❑ Renal, hepatic, hematological (including sickle cell disease) or metabolic disorders (including diabetes mellitus) ❑ Neurologic and neurodevelopment conditions (including disorders of the brain, spinal cord, peripheral nerve, and muscle such as cerebral palsy, epilepsy, stroke, intellectual disability (mental retardation), moderate to severe developmental delay, muscular dystrophy, or spinal cord injury) ❑ Persons with immunosuppression, including that caused by medications or by HIV infection ❑ Women who are pregnant or postpartum (within 2 weeks after delivery) ❑ Children and adolescents through 18 years who are receiving aspirin- or salicylate-containing medications and who might be at risk for experiencing Reye syndrome after influenza virus infection ❑ American Indians/Alaska Natives ❑ Persons who are morbidly obese (BMI ≥40 kg/m2) ❑ Residents of nursing homes and other chronic-care facilities.

Examine the patient: Appearance ❑ Fatigue Vital signs ❑ Fever ❑(100-104° F) ❑ Heart rate ❑ Tachycardia ❑ Respiratory rate ❑ Tachypnea Skin ❑ Flushing may be present ❑ Rash may be present ❑ Increased sweating Eyes ❑ Watery eyes ❑ Redness Nose ❑ Nasal congestion ❑ Runny nose Throat ❑ Erythema and inflammation may be present ❑ Pharyngitis Lungs ❑ Usually, lung examination is normal ❑ Findings of severe disease include: ❑ Dry cough ❑ Rales ❑ Focal wheezing

Shown below is an algorithm summarizing the diagnostic approach of Influenza according to the the Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenza.

Which Patients Should Be Tested for Influenza?

During influenza activity

During low influenza activity

Outpatients (including emergency department patients)

Hospitalized Patients

Outpatients

Hospitalized Patients

❑ High-risk patients, including immunocompromised persons who present with influenza-like illness, pneumonia, or nonspecific respiratory illness (eg, cough without fever) if the testing result will influence clinical management ❑ patients who present with acute onset of respiratory symptoms with or without fever, and either exacerbation of chronic medical conditions (eg, asthma, chronic obstructive pulmonary disease, heart failure) or known complications of influenza (eg, pneumonia) if the testing result will influence clinical management ❑ Patients not at high risk for influenza complications who present with influenza-like illness, pneumonia, or nonspecific respiratory illness (eg, cough without fever) and who are likely to be discharged home if the results might :❑ influence antiviral treatment decisions or  :❑ reduce use of unnecessary antibiotics,  :❑ reduce further diagnostic testing, and  :❑ reduce time in the emergency department, or  :❑ influence antiviral treatment or chemoprophylaxis decisions for high-risk household contacts.

❑ All patients requiring hospitalization with acute respiratory illness, including pneumonia, with or without fever ❑ All patients with acute worsening of chronic cardiopulmonary disease (eg, COPD, asthma, coronary artery disease, or heart failure), as influenza can be associated with exacerbation of underlying conditions ❑ All patients who are immunocompromised or at high risk of complications and present with acute onset of respiratory symptoms with or without fever, as the manifestations of influenza in such patients are frequently less characteristic than in immunocompetent individuals ❑ All patients who, while hospitalized, develop acute onset of respiratory symptoms, with or without fever, or respiratory distress, without a clear alternative diagnosis

❑ Patients with acute onset of respiratory symptoms with or without fever, especially for immunocompromised and high-risk patients

❑ All patients requiring hospitalization with acute respiratory illness, with or without fever, who have an epidemiological link to a person diagnosed with influenza, an influenza outbreak or outbreak of acute febrile respiratory illness of uncertain cause, or who recently traveled from an area with known influenza activity. ❑ Patients with acute, febrile respiratory tract illness, especially children and adults who are immunocompromised or at high risk of complications, or if the results might influence antiviral treatment or chemoprophylaxis decisions for high-risk household contacts

Does the patient have signs and symptoms suggestive of influenza?

Yes

No

Does the patient have atypical signs and symptoms or complications associated with influenza

Is the patient being admitted to the hospital?

Yes

No

Yes

No

Will testing results influence clinical management?

Influenza testing not indicated; consider other etiologies and treatments, discharge home

Yes

No

Test for influenza; start empiric antiviral treatment while results are pending

Influenza clinically diagnosed; start empiric antiviral therapy if the patient is in high risk group for complications, has progressive disease, discharge home

Influenza virus testing methods:

Method	Types Detected	Acceptable Specimens	Time to Results	Performance
Rapid Influenza Diagnostic Tests (Antigen detection)	A and B	Nasopharyngeal swab Throat swab Nasal wash Nasal aspirate Sputum	<15 min	Low to moderate sensitivity; high specificity;
Rapid Molecular Assay (Influenza viral RNA or nucleic acid detection)	A and B	Nasopharyngeal swab Nasal wash	15-30 minutes	High sensitivity; high specificity
Immunofluorescence, Direct (DFA) or Indirect (IFA) Antibody Staining (Antigen detection)	A and B	Nasopharyngeal swab or wash Bronchial wash Nasal or endotracheal aspirate	1-4 hours	Moderate sensitivity; high specificity
RT-PCR and other molecular assays (Nucleic acid detection)	A and B	Nasopharyngeal swab Throat swab Nasopharyngeal or bronchial wash Nasal or endotracheal aspirate Sputum	Varied (Generally 1-8 hours)	High sensitivity; high specificity
Rapid cell culture (shell vials; cell mixtures) (Virus isolation)	A and B	Nasopharyngeal swab Throat swab Nasopharyngeal or bronchial wash Nasal or endotracheal aspirate Sputum	1-3 days	High sensitivity; high specificity
Viral culture (conventional) (Virus isolation)	A and B	Nasopharyngeal swab Throat swab Nasopharyngeal or bronchial wash Nasal or endotracheal aspirate Sputum	3-10 days	High sensitivity; high specificity
Table adapted from: Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenza CDC Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests

Does the patient have signs and symptoms suggestive of influenza?

Yes

No

Does the patient have atypical signs and symptoms or complications associated with influenza

Is the patient being admitted to the hospital?

Yes

No

Yes

No

Will testing results influence clinical management?

Influenza testing not indicated; consider other etiologies and treatments, discharge home

Yes

No

Test for influenza; start empiric antiviral treatment while results are pending

Influenza clinically diagnosed; start empiric antiviral therapy if the patient is in high risk group for complications, has progressive disease, discharge home

Treatment

Symptomatic Relief

OTC medicines provide relief for 'flu symptoms

Symptom(s)	OTC Medicine
Fever, Aches, Pains, Sinus pressure, Sore throat	Analgesics
Nasal congestion, Sinus pressure	Decongestants
Sinus pressure, Runny nose, Watery eyes, Cough	Antihistamines
Cough	Cough suppressant
Sore throat	Local anesthetics

Do's and Dont's

• Children and teenagers with flu symptoms (particularly fever) should avoid taking aspirin as taking aspirin in the presence of influenza infection (especially Influenzavirus B) can lead to Reye's syndrome, a rare but potentially fatal disease of the liver.