InfluenzaMANAGEMENT

INFECTIOUS DISEASE PRESENTATIONS · 12 SECTIONS

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490 items

☷ Legend

01Approach to the Critical Patient/attcp63

Immediate threats

›Resuscitation priorities

›Airway risk

›Stridor

›Inability to protect airway

›Altered mental status

›Breathing failure

›SpO2 persistently low despite supplemental oxygen

›Rising work of breathing

›Exhaustion

›Circulatory shock

›Hypotension

›Mottling

›Lactate elevation with hypoperfusion concern

›High consequence complications

›Severe pneumonia

›Myocarditis

›Encephalopathy

›Secondary bacterial sepsis

Infection control

›Transmission controls

›Droplet precautions

›Surgical mask for staff and patient

›Eye protection for close contact

›Airborne precautions triggers

›Aerosol generating procedures

›Intubation

›Nebulized therapy

Early treatment decision points

›Antiviral treatment triggers

›Hospital admission planned

›Antiviral therapy regardless of time since symptom onset

›High risk for complications

›Age under 5 years

›Age 65 years or older

›Pregnancy and up to 2 weeks postpartum

›Chronic pulmonary disease

›Cardiovascular disease excluding isolated hypertension

›Chronic kidney disease

›Chronic liver disease

›Diabetes mellitus

›Immunocompromised state

›Neurologic or neurodevelopmental conditions

›BMI 40 kg/m2 or higher

›Otherwise healthy outpatient within 48 hours

›Symptom onset 48 hours or less

Supportive care targets

›Physiologic targets

›Oxygenation

›SpO2 goal 92% or higher

›Chronic hypercapnia individualized SpO2 goal

›Hydration

›Euvolemia

›Oral rehydration when tolerated

›Fever and pain control

›Acetaminophen dosing per local formulary

›NSAID use per comorbidity profile

Consultation triggers

›Escalation pathways

›Critical care

›Persistent hypoxemia

›Noninvasive ventilation requirement

›Intubation requirement

›Shock

›Infectious diseases

›Immunocompromised with prolonged viral shedding concern

›Suspected antiviral resistance

›Severe influenza with multi organ involvement

02History/hx65

Symptom pattern and timing

›Illness timeline

›Symptom onset date and time

›Under 48 hours

›Over 48 hours

›Fever pattern

›Persistent fever over 3 days

›Recurrent fever after improvement

›Respiratory symptoms

›Cough

›Sore throat

›Rhinorrhea

›Dyspnea

›Pleuritic pain

›Systemic symptoms

›Myalgias

›Headache

›Profound fatigue

›Gastrointestinal symptoms

›Vomiting

›Diarrhea

Risk and exposure

›Exposure context

›Household influenza like illness

›High risk household members

›Outbreak setting

›Long term care

›Shelter

›Correctional facility

›School or daycare cluster

›Occupational exposure

›Healthcare

›Childcare

›Travel exposure

›Recent travel with respiratory outbreaks

›Host risk factors

›Pregnancy status

›Postpartum within 2 weeks

›Chronic lung disease

›Asthma

›COPD

›Cardiac disease

›Immunosuppression

›Renal disease

›Diabetes

›Neuromuscular disease

›Frailty and baseline function

Red flag symptoms

›Danger features

›Chest pain

›Exertional component

›Syncope

›Severe dyspnea

›Confusion

›Focal neurologic symptoms

›Inability to maintain hydration

›Cyanosis

›Hemoptysis

Medication and prevention

›Treatment history

›Antiviral use prior to arrival

›Dose and start time

›Antibiotic use prior to arrival

›Antipyretic response

›Prevention history

›Current season influenza vaccination status

›Vaccinated

›Not vaccinated

›Unknown

03Physical Exam/exam43

Vitals and general

›Severity markers

›Temperature

›Persistent fever

›Hypothermia

›Heart rate

›Tachycardia out of proportion to fever

›Blood pressure

›Hypotension

›Respiratory rate

›Tachypnea

›SpO2 on room air

›Hypoxemia

›Mental status

›Delirium

›Lethargy

›Hydration status

›Dry mucous membranes

›Capillary refill

›Orthostasis

Respiratory

›Lung assessment

›Work of breathing

›Accessory muscle use

›Inability to speak full sentences

›Auscultation

›Focal crackles

›Diffuse wheeze

›Decreased breath sounds

›Upper airway

›Stridor

›Voice change

Cardiovascular and neurologic

›Cardiac findings

›New murmur

›Gallop rhythm

›Signs of heart failure

›Neurologic findings

›Meningismus

›Focal deficits

›Seizure activity

PITFALLS

›Missed complications

›Normal lung exam early in pneumonia

›Older adults with minimal fever

›Children with primary dehydration presentation

›Secondary bacterial pneumonia after initial improvement

04Differential Diagnosis/ddx26

Viral and atypical respiratory

›Respiratory viral syndromes

›COVID-19

›Overlapping influenza like illness

›RSV infection

›Parainfluenza

›Human metapneumovirus

›Atypical pneumonias

›Mycoplasma pneumonia

›Chlamydophila pneumonia

Bacterial and high risk mimics

›Bacterial infections

›Community acquired pneumonia

›Streptococcus pneumoniae

›Staphylococcus aureus including MRSA

›Haemophilus influenzae

›Streptococcal pharyngitis

›Pertussis

›Life threatening mimics

›Sepsis syndrome

›Pulmonary embolism

›Acute coronary syndrome

›Meningitis

Coding aligned problem list

›Influenza coding anchors

›ICD-10 J09 influenza due to identified zoonotic or pandemic influenza virus

›ICD-10 J10 influenza due to other identified influenza virus

›ICD-10 J11 influenza due to unidentified influenza virus

›SNOMED CT influenza infection concept

05Laboratory Tests/lt23

Core labs by severity

›Baseline assessment

›Complete blood count for severe illness

›Leukocytosis secondary bacterial infection concern

›Leukopenia immunosuppression marker

›Electrolytes and renal function for dehydration and dosing

›Creatinine clearance estimation for oseltamivir adjustment

›Hyponatremia in severe infection concern

›Liver enzymes for systemic illness

›Hepatic dysfunction for differential and medication safety

›Sepsis and organ dysfunction

›Lactate for shock concern

›Serial trend for resuscitation response

›Blood cultures for pneumonia or sepsis concern

›Before antibiotics when feasible

›Venous blood gas for respiratory failure assessment

›pCO2 in mmHg

›Targeted labs for complications

›Troponin for myocarditis concern

›Serial testing if ongoing symptoms

›Creatine kinase for myositis or rhabdomyolysis concern

›Kidney injury risk linkage

›Pregnancy test when status uncertain

›Antiviral and imaging planning

06Diagnostic Tests/dt54

Scoring Systems

›Risk stratification tools

›NEWS2 for clinical deterioration risk

›Escalation thresholds per local protocol

›qSOFA for sepsis risk screen

›Altered mentation

›Respiratory rate 22 per minute or higher

›Systolic blood pressure 100 mmHg or lower

›CURB-65 for pneumonia disposition support

›Confusion

›Urea

›Respiratory rate 30 per minute or higher

›Blood pressure low threshold

›Age 65 years or older

›IDSA ATS severe CAP criteria for ICU consideration

›Major criteria

›Minor criteria count

MRI

›Neurologic complications imaging

›MRI brain indications

›Encephalitis concern

›Persistent altered mental status without alternative explanation

›MRI brain findings

›Temporal lobe signal abnormalities

›Diffuse inflammatory changes

›MRI limits

›Not a primary influenza diagnostic test

›Time and stability requirements

›Pulmonary and complication imaging

›CT chest indications

›Severe hypoxemia with nondiagnostic chest radiograph

›Suspected pulmonary embolism

›Suspected empyema or necrotizing pneumonia

›CT head indications

›Focal neurologic deficits

›Concern for intracranial complication

›CT limits

›Viral pneumonia imaging nonspecific

›Radiation and contrast risk tradeoffs

Ultrasound

›Point of care ultrasound applications

›Lung ultrasound

›Focal consolidation for bacterial pneumonia support

›Pleural effusion detection

›Cardiac ultrasound

›Global systolic function for myocarditis concern

›Pericardial effusion assessment

›IVC ultrasound

›Volume status adjunct

Virologic testing

›Influenza specific testing

›NAAT RT-PCR

›Highest sensitivity among routine options

›Preferred for hospitalized and high risk

›Rapid influenza diagnostic tests

›Sensitivity approximately 50% to 70% with wide range

›Specificity approximately 90% to 99%

›False negatives more likely when community prevalence high

07Disposition/dispo30

Discharge criteria

›Safe outpatient pathway

›Clinical stability

›Normal mentation

›No respiratory distress

›SpO2 stable on room air or baseline oxygen

›Hydration adequacy

›Oral intake tolerated

›No persistent vomiting

›Follow up feasibility

›Reliable access within 24 to 48 hours

›Return precautions understood

›Antiviral plan

›High risk and treatment initiated or arranged

Admission criteria

›Inpatient indications

›Hypoxemia requiring supplemental oxygen

›Moderate to severe respiratory distress

›Hemodynamic instability

›Altered mental status

›Severe dehydration or unable to maintain intake

›Significant comorbidity decompensation

›Complication concern

›Pneumonia

›Myocarditis

›Encephalitis

ICU criteria

›Critical care indications

›Mechanical ventilation requirement

›Persistent hypoxemia despite high flow oxygen

›Shock requiring vasopressors

›Rapid clinical deterioration

›Severe CAP criteria met

08Treatment/t90

Supportive care

›Symptom and physiologic support

›Oxygen therapy

›Nasal cannula for mild hypoxemia

›High flow nasal oxygen for escalating needs

›Noninvasive ventilation for selected patients

›Intubation if failing noninvasive support

›Fluids

›Oral rehydration for mild dehydration

›IV crystalloids for significant dehydration or shock

›Antipyretics and analgesia

›Acetaminophen per local formulary

›NSAID per renal and GI risk

›Antiemetics

›Persistent vomiting with dehydration risk

Antiviral therapy

›Neuraminidase and endonuclease inhibitors

›Timing and priority

›Initiate as soon as possible for hospitalized and high risk

›Most benefit when started within 48 hours in uncomplicated outpatient illness

›Longer duration for severe or immunocompromised may be needed

›Oseltamivir oral

›Adults treatment

›75 mg twice daily for 5 days

›Extend duration for severe illness per clinical judgment

›Children treatment

›Under 1 year

›3 mg/kg per dose twice daily for 5 days

›1 year or older weight based

›15 kg or less 30 mg twice daily

›Over 15 kg to 23 kg 45 mg twice daily

›Over 23 kg to 40 kg 60 mg twice daily

›Over 40 kg 75 mg twice daily

›Chemoprophylaxis

›Adults

›75 mg once daily for 7 days after last exposure

›Children 3 months to under 1 year

›3 mg/kg per dose once daily

›Children under 3 months

›Not recommended unless situation judged critical

›Children 1 year or older weight based

›15 kg or less 30 mg once daily

›Over 15 kg to 23 kg 45 mg once daily

›Over 23 kg to 40 kg 60 mg once daily

›Over 40 kg 75 mg once daily

›Zanamivir inhaled

›Contraindication considerations

›Underlying airway disease

›Asthma

›COPD

›Treatment

›10 mg as two inhalations twice daily for 5 days

›Age 7 years or older

›Chemoprophylaxis

›10 mg as two inhalations once daily for 7 days

›Age 5 years or older

›Peramivir IV

›Treatment single dose

›Adults and age 13 years or older

›600 mg IV once infused over at least 15 minutes

›Age 6 months to 12 years

›12 mg/kg IV once

›Maximum 600 mg

›Infusion at least 15 minutes

›Chemoprophylaxis

›Not recommended

›Baloxavir oral

›Treatment single dose

›Age 5 years and older under 20 kg

›2 mg/kg once

›Weight 20 kg to under 80 kg

›40 mg once

›Weight 80 kg or higher

›80 mg once

›Post exposure prophylaxis

›Age 5 years and older

›Same dosing as treatment

Antibiotics and complications

›Bacterial coinfection management

›Empiric antibiotics triggers

›Radiographic pneumonia

›Sepsis physiology

›Marked focal lung findings

›Recurrent fever after improvement

›MRSA coverage triggers

›Severe CAP with necrotizing features

›Hemoptysis

›ICU level pneumonia

Therapies to avoid

›Harm reduction

›Systemic corticosteroids for influenza without another indication

›Avoid routine use

›Antibiotics for uncomplicated influenza without bacterial concern

›Stewardship

09Special Populations/sp29

Pregnancy

›Maternal fetal considerations

›Higher risk of severe influenza and complications

›Lower threshold for treatment and admission

›Antiviral selection

›Oseltamivir preferred in pregnancy

›Most safety data among antivirals

›Chemoprophylaxis after close contact

›Oseltamivir 75 mg once daily for 7 days after last exposure

›Breastfeeding

›Oseltamivir compatible

›Less than 1% excreted in breast milk

Geriatric

›Older adult risks

›Atypical presentation

›Minimal fever

›Delirium as primary symptom

›Antiviral prioritization

›Treat regardless of time since onset when hospitalized or high risk

›Vaccination preference age 65 years or older

›High dose inactivated vaccine option

›Recombinant vaccine option

›Adjuvanted inactivated vaccine option

Pediatrics

›Child specific considerations

›Higher dehydration risk

›Early oral rehydration strategy

›Antiviral age thresholds

›Oseltamivir approved and used down to infancy dosing guidance

›Peramivir age 6 months or older

›Baloxavir age 5 years or older

›Zanamivir age 7 years or older for treatment

10Background/b29

Epidemiology

›Seasonal patterns and prevention

›Annual vaccination recommendation

›Canada vaccine offered annually to age 6 months and older without contraindication

›2025 to 2026 vaccine composition

›Trivalent formulation

›A H1N1 component

›A H3N2 component

›B Victoria lineage component

Pathophysiology

›Disease mechanism

›Influenza A and B viral replication in respiratory epithelium

›Epithelial injury

›Cytokine mediated systemic symptoms

›Complication pathways

›Viral pneumonia with diffuse alveolar damage

›Secondary bacterial pneumonia from mucociliary dysfunction

›Myocarditis from inflammatory injury

›Encephalopathy from systemic and direct effects

Therapeutic Considerations

›Evidence framework

›Antivirals shorten illness and reduce complications in high risk populations when started early

›Treatment recommended for uncomplicated ambulatory illness

›Oseltamivir 5 days

›IDSA A-I

›Zanamivir 5 days

›IDSA A-I

›Peramivir single dose

›IDSA A-I

›Testing limitations

›RIDT false negatives common during high community activity

›Negative RIDT does not exclude influenza in compatible illness

11Patient Discharge Instructions/pdi27

copy discharge instructions

›Home care plan

›Hydration

›Frequent oral fluids

›Oral rehydration solution if vomiting or diarrhea

›Fever and pain control

›Acetaminophen per label directions

›NSAID per label directions if safe for kidneys and stomach

›Infection prevention

›Mask around others when symptomatic

›Hand hygiene

›Avoid close contact with high risk people until improving

›Antiviral adherence when prescribed

›Complete full course

›Return to ED immediately

›Trouble breathing

›Blue or grey lips

›Chest pain

›New confusion

›Fainting

›Signs of dehydration

›No urination for 8 hours

›Unable to keep fluids down

›Fever or symptoms improving then suddenly worsening

›Severe weakness preventing normal activity

›Follow up

›Primary care within 24 to 48 hours if high risk

›Earlier follow up for worsening cough or dyspnea

12References/r11

Clinical guidelines and public health

›CDC influenza antiviral medications summary for clinicians

›CDC antiviral dosing table for treatment and chemoprophylaxis

›IDSA seasonal influenza clinical practice guideline

›CDC rapid influenza diagnostic tests clinician guidance

›CDC ACIP influenza vaccine recommendations summary

›NACI statement on seasonal influenza vaccines 2025 to 2026

›ACOG influenza in pregnancy prevention and treatment practice advisory

›Ontario Health recommendations for antiviral therapy of seasonal influenza

Evidence grading notes

›IDSA uses graded recommendations including A-I strength and quality

›ACEP Level A B C policy statements not identified for seasonal influenza antiviral selection

›Class I IIa IIb terminology not routinely used in influenza guidelines

Evidence & Review

Reviewed by SymptomDx Medical Team · Last reviewed June 16, 2026

SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.