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Level 2 of 6Must-remember

Influenza, COVID-19 and viral respiratory infection

Assess, manage and stay safe — enough on its own

The card — assess, manage, caution

Assessment— look, ask, measure

  • Two numbers govern the acute assessment: the interval since symptom onset, and the oxygen saturation with the inspired oxygen recorded beside it — record both before anything else, because they decide the antiviral and the escalation.
  • Ask about the tempo of onset: influenza begins abruptly and patients can often name the hour, with fever, rigors, myalgia (frequently severe, sometimes the dominant complaint), fatigue, headache, sore throat and dry cough dominating the first two to three days and coryza less prominent than in a common cold; COVID-19 onset is often more gradual, with fever, chills, cough, breathlessness, fatigue, sore throat, headache, myalgia, anosmia or dysgeusia (relatively specific when present) and gastrointestinal symptoms in varying combinations.
  • Use the clinical rule for influenza: fever above 38.2 °C with cough during influenza season is highly predictive of influenza in anyone older than 4 years, and when community influenza-like-illness activity is high, clinical diagnosis based on cough, fever, chills, myalgia and acute onset has a positive predictive value of around 70%.
  • Take the exposure history, because the epidemiology makes the diagnosis when the clinical picture cannot: contact with poultry, live-bird markets, sick or dead birds, culling work or dairy cattle raises avian influenza (H5N1, H7N9 and other H5, H7 and H9 subtypes); travel to the Middle East or contact with dromedary camels raises MERS-CoV, case fatality approximately 35%; and ask about household cases, since household attack rates are high — over 50% in early SARS-CoV-2 studies.
  • Identify the host risk factors for severe disease: age 65 and over (more than 95% of COVID-19 deaths occurred in people over 45 and more than 80% in those over 65, and at least 64% of pneumonia-and-influenza deaths occur in older people, who are only about 16% of the population); age under 5, especially under 2; chronic lung disease, particularly COPD, the single most profound risk factor; chronic heart, liver, kidney and neurological disease and diabetes; immunosuppression; pregnancy and the two weeks post-partum; obesity (a 113% increased risk in one large hospitalised COVID-19 cohort); smoking; and institutional living.
  • Examine deliberately: count the respiratory rate over a full 15 seconds or longer, assess work of breathing, ability to complete a sentence and conscious level, and record the oxygen saturation with the inspired oxygen alongside it; wheeze in an adult with a viral illness is a real finding, since rhinovirus, RSV and hMPV all precipitate exacerbations of asthma and COPD.
  • Examine the calves and the jugular venous pressure — pulmonary embolism and heart failure are the look-alikes most often missed, and hypoxaemia out of proportion to the chest film with a clear chest and unilateral leg swelling should trigger imaging, particularly in COVID-19.
  • Treat any of these as requiring emergency assessment rather than reassurance: moderate-to-severe dyspnoea; cyanosis; change in mental status; chest pain; and reduced urine output or anuria — with or without an oxygen saturation of 94% or less; add inability to complete a sentence, exhaustion, and the ominous combination of a falling respiratory rate with a rising carbon dioxide, which is impending respiratory arrest, not improvement.
  • Apply the hospitalisation thresholds: oxygen saturation on room air below 94%, respiratory rate over 30 breaths/min, PaO₂/FiO₂ ratio below 300 mmHg, or chest radiograph infiltrates over 50% of lung fields — these serve as a general severity frame for viral pneumonitis of any cause.Not available at your setup — Arterial blood gas. Without blood gas, use SpO2, respiratory rate and chest radiograph infiltrates alone.
  • Calculate the P/F ratio correctly: PaO₂ in mmHg divided by FiO₂ as a decimal (room air 0.21; a reservoir mask at 15 L/min approximates 0.85); if the analyser reports kPa, multiply by 7.5 first; a ratio below 300 marks severe disease and a ratio of 250 or below a patient likely to need ventilatory support.Not available at your setup — Arterial blood gas.
  • Grade COVID-19 severity: mild (symptoms without dyspnoea or abnormal imaging), moderate (lower respiratory disease with SpO₂ at or above 94% on air), severe (any threshold above met) and critical (respiratory failure, septic shock or multi-organ dysfunction) — about 80% of symptomatic patients have mild disease and approximately 5% develop respiratory failure, shock and multi-organ failure.
  • Use CURB-65 with its known limitation — one point each for Confusion, Urea over 7 mmol/L, Respiratory rate at least 30/min, Blood pressure (systolic below 90 or diastolic 60 mmHg or less) and age at least 65; 0–1 low severity, 2 intermediate, 3–5 high — but remember it was derived in bacterial community-acquired pneumonia and systematically underestimates severity in viral pneumonitis, where profound hypoxaemia coexists with normal blood pressure, normal urea and preserved mentation; an aggregate early-warning score such as NEWS2 better tracks trajectory over hours.
  • Count the paediatric respiratory rate for a full minute in a quiet child: fast breathing is at least 60/min under 2 months, 50/min at 2–11 months, 40/min at 1–5 years and 30/min above 5 years; red flags, any one of which indicates severe disease, are lower chest wall indrawing, grunting, nasal flaring, central cyanosis, SpO₂ below 90%, inability to drink or feed, convulsions, lethargy, apnoea (especially under 3 months), and a heart rate that falls as the child tires.
  • Do not be reassured by comfort or by a normal temperature: a recurring feature of COVID-19 is the comfortable, conversational patient saturating 88% — absence of distress is not evidence of adequate gas exchange; and in the elderly fever may be absent and cough unimpressive, influenza and COVID-19 presenting as new confusion or delirium, an unexplained fall, immobility, anorexia, or simply decompensation of a chronic cardiac or respiratory illness.
  • Know the three paediatric syndromes: bronchiolitis, usually RSV — coryza then tachypnoea, wheeze, air trapping, poor feeding and, critically, apnoea, which is what kills small infants, not wheeze (30–70% of RSV infections in infants and young children progress to lower respiratory involvement); croup, usually parainfluenza — barking cough, hoarseness and inspiratory stridor; and measles in the unimmunised — three or more days of high fever with the 3 Cs (cough, coryza, conjunctivitis), then a maculopapular rash and Koplik's spots, needing airborne isolation, with roughly 1 in 1000 affected children developing encephalitis.
  • Expect a different picture in the immunocompromised: illness may begin as an ordinary-sounding cold and progress to chronic, relapsing or fatal lower respiratory infection, shedding is prolonged, antiviral resistance may emerge on treatment, and reactivated cytomegalovirus, herpes simplex or adenovirus may complicate the picture.

Management— do this, in order

  • Isolate before you take the history. Standard plus droplet and contact precautions in an individual room suffice for most respiratory viruses; airborne precautions are required for suspected measles or varicella, for high-consequence pathogens such as avian influenza and MERS-CoV, and for any aerosol-generating procedure — bronchoscopy, intubation, open suctioning, nebulised medication, non-invasive ventilation and high-flow nasal oxygen — needing an FFP2/N95-equivalent respirator, eye protection, gown and gloves; give bronchodilators by inhaler and spacer rather than nebuliser wherever possible.
  • Give oxygen immediately and titrate afterwards: target SpO₂ 94–98% in most adults; the single exception is known or suspected chronic type 2 respiratory failure, where the target is 88–92%, ideally by Venturi device. Oxygen should never be withheld from a peri-arrest patient for fear of carbon dioxide retention, and in children there is no hypoxic-drive concern.
  • Escalate the device rather than merely the flow: nasal cannulae, then simple mask, then Venturi mask, then reservoir mask at 15 L/min, then high-flow nasal oxygen or non-invasive ventilation, then invasive ventilation — and because hypoxaemic viral pneumonitis fails non-invasive support frequently and a prolonged failing trial that delays intubation worsens outcome, set the decision point in advance by a time limit and objective targets.
  • Consider awake proning for 30 minutes to 2 hours at a time in a cooperative, stable hypoxaemic patient with COVID-19 — it may improve oxygenation but is an adjunct rather than a substitute for escalation.
  • Give a balanced crystalloid or 0.9% sodium chloride 500 mL intravenously over 15 minutes to a hypotensive adult (10–20 mL/kg in a child) — but these are wet, inflamed lungs, so re-examine the chest and jugular venous pressure after every bolus.Doctor / Nurse
  • Give paracetamol 1 g orally or intravenously 6-hourly (maximum 4 g/24 h); in children paracetamol 15 mg/kg per dose orally 4–6 hourly (maximum 4 doses/24 h) or ibuprofen 5–10 mg/kg per dose 6–8 hourly with food; and remember that agitation in a hypoxaemic patient is hypoxaemia until proved otherwise.Doctor / Nurse
  • Give oseltamivir 75 mg orally or by nasogastric tube twice daily for 5 days as first-line influenza treatment to everyone hospitalised, severely ill, deteriorating or with complicated infection regardless of illness duration, and to anyone at high risk of complications with a suggestive presentation or positive test — start it without waiting for the swab; reduce in renal impairment (commonly 30 mg twice daily for creatinine clearance 30–60 mL/min, 30 mg once daily for 10–30 mL/min), and consider 10 days in severe illness with persistent shedding.
  • Use the paediatric oseltamivir doses, twice daily for 5 days: infant under 1 year 3 mg/kg per dose; 15 kg or less 30 mg; over 15–23 kg 45 mg; over 23–40 kg 60 mg; over 40 kg 75 mg.
  • Know the alternatives and their limits: zanamivir 10 mg (two 5 mg inhalations) twice daily for 5 days from age 7 — uncomplicated influenza only; peramivir 600 mg IV as a single dose (adults 18 and over, from age 2 for symptoms of 2 days or less; 200 mg in renal dysfunction) when oral absorption is in doubt; baloxavir marboxil 40 mg orally once if under 80 kg, 80 mg once if 80 kg or more, within 48 hours of onset, from age 12; amantadine and rimantadine are not recommended, resistance being near-universal with no activity against influenza B.Doctor / NurseNot available at your setup — Infusion pump. If IV peramivir cannot be given, use oral oseltamivir instead.
  • Treat COVID-19 at risk of progression early: nirmatrelvir 300 mg with ritonavir 100 mg, both orally twice daily for 5 days, started within 5 days of onset (nirmatrelvir 150 mg if eGFR 30–59 mL/min/1.73 m², not recommended below 30, licensed from age 12 and 40 kg) — review the whole drug list first, because ritonavir has extensive, dangerous interactions with statins, amiodarone, rifampicin, carbamazepine, direct oral anticoagulants and calcineurin inhibitors.
  • Or use remdesivir 200 mg IV on day 1 then 100 mg IV daily — a 3-day course — within 7 days of onset if aged 60 or over or comorbid; or molnupiravir 800 mg orally every 12 hours for 5 days within 5 days of onset, reserving molnupiravir for when the others are unusable and remembering it is contraindicated in pregnancy and under 18 years.Doctor / NurseNot available at your setup — Infusion pump. If IV remdesivir is unavailable, use oral molnupiravir instead (not in pregnancy or under 18).
  • In the hypoxaemic COVID-19 inpatient give dexamethasone 6 mg orally or intravenously once daily for up to 10 days, or until discharge if sooner, to any patient requiring supplemental oxygen — equivalents are prednisolone 40 mg orally daily, methylprednisolone 32 mg daily or hydrocortisone 160 mg daily in divided doses — and add tocilizumab or baricitinib in patients on oxygen or ventilation already receiving dexamethasone, with no super-infection and a CRP above 75 mg/L.Doctor / Nurse
  • Give pharmacological venous thromboembolism prophylaxis to every patient hospitalised with COVID-19 unless strongly contraindicated; outpatients should not receive it.
  • Treat the bacterial exception: influenza with lobar consolidation, or with fever recurring after day 4 alongside productive cough and a white cell count above 10 × 10⁹/L, needs cover against *Streptococcus pneumoniae* and *Staphylococcus aureus* — superinfection complicates as many as 10% of influenza pneumonias and most influenza deaths are bacterial; take blood cultures before any antibacterial.Not available at your setup — Blood culture.
  • In suspected avian influenza give oseltamivir immediately — modelling associates it with a 49% reduction in H5N1 mortality — use the highest available respiratory protection, warn the laboratory before the specimen leaves the bedside, and notify public health; seasonal influenza vaccine confers no cross-protection against H5, H7 or H9 strains.
  • In pregnancy, where influenza pneumonia carries high mortality, oseltamivir is the antiviral of choice — treat early and admit at a low threshold; molnupiravir is contraindicated, and both influenza and COVID-19 vaccination are recommended in pregnancy.
  • Give post-exposure chemoprophylaxis, which prevents 70–90% of influenza infections, to close contacts at high risk of complications or after unprotected occupational exposure: oseltamivir 75 mg orally once daily or zanamivir 10 mg inhaled once daily, continued through 7 days after the last exposure — breakthrough illness needs treatment doses, and hand hygiene and surgical masks prevent household transmission when started within 36 hours of symptom recognition in the index case.
  • Set the duration of precautions: for influenza isolate until 7 days from onset or 24 hours after symptom resolution, whichever is longer; for COVID-19 at home, until fever-free for 24 hours without antipyretics and improving.

Caution— what harms

  • Never give aspirin to a child or adolescent with influenza or varicella, because of Reye's syndrome.
  • Never treat severe influenza with inhaled zanamivir: it is for uncomplicated influenza only, is relatively contraindicated in asthma and COPD because of bronchospasm, lacks efficacy in pneumonia, and is not formulated for ventilated patients.
  • Never give corticosteroids for influenza pneumonia, which may be associated with higher mortality — the mirror image of the COVID-19 rule and the commonest cross-contamination error in contemporary practice; asthma and COPD remain independent indications.
  • Do not give corticosteroids to a COVID-19 patient who does not require oxygen — there is no benefit and there is harm.
  • Do not trust CURB-65 in viral pneumonitis: it systematically underestimates severity, since profound hypoxaemia coexists with normal blood pressure, normal urea and preserved mentation — assess oxygenation independently and track trajectory with NEWS2.
  • Do not treat a negative rapid antigen test as a well patient: rapid antigen tests are quicker and less sensitive, a negative rapid test during a known outbreak in a patient with a convincing picture does not exclude influenza — treat anyway — and rapid assays cannot distinguish avian from seasonal influenza and are neither sensitive nor specific for H5N1.
  • Do not treat a positive PCR as proof of active infection: viral genome persists in nasal secretions for weeks after clinical resolution, particularly in the immunocompromised, which is why retesting for SARS-CoV-2 within 90 days of documented infection is discouraged; conversely an upper airway swab may be negative when the virus is confined to the lower tract, so send a lower respiratory specimen where viral pneumonia is suspected.
  • Do not read a falling respiratory rate as improvement: a *falling* respiratory rate with a *rising* carbon dioxide is impending respiratory arrest, and a normal or rising PaCO₂ in a tachypnoeic hypoxaemic patient signifies fatigue and is a pre-terminal sign unless chronic hypercapnia is known.
  • Do not persist with a failing trial of non-invasive support: hypoxaemic viral pneumonitis fails it frequently and delayed intubation worsens outcome — and never let awake proning substitute for escalation.
  • Do not nebulise casually: nebulised medication, non-invasive ventilation, high-flow nasal oxygen, bronchoscopy, intubation and open suctioning are aerosol-generating procedures requiring airborne precautions; give bronchodilators by inhaler and spacer wherever possible.
  • Do not give antibiotics reflexively: they do not improve the outcome of uncomplicated respiratory virus infection in otherwise healthy people, and bacterial co-infection occurs in approximately 8% of hospitalised COVID-19 patients — take cultures first, treat when the diagnosis is genuinely uncertain or the patient severely hypoxaemic, and review at 48 hours intending to stop.
  • Do not give a neuraminidase inhibitor or baloxavir within 2 days before, or 2 weeks after, a live attenuated influenza vaccine, which it will inactivate; and remember antivirals are additive to antibacterials, not alternative to them — a patient with community-acquired pneumonia in whom influenza is detected needs both.
  • Do not withdraw established immunosuppression abruptly — it is a case-by-case decision for the treating specialist, and adrenal crisis can kill faster than the virus; and do not use aerosolised ribavirin for RSV, whose efficacy remains uncertain, bronchiolitis being managed with oxygen, feeding support, nasal suction and observation for apnoea.
  • Do not let the season cost you another diagnosis: malaria is easily confused with influenza early, so send a blood film; ask every young patient with a viral-looking pneumonitis about vaping; and consider pulmonary embolism, acute coronary syndrome (myocardial infarction occurred in 14% of patients with COVID-19 in one multicentre cohort), heart failure, tuberculosis and *Pneumocystis* pneumonia.

Refer / escalate

Escalate or transfer for an oxygen saturation below 94% on room air, a respiratory rate over 30 breaths/min, a PaO₂/FiO₂ ratio below 300 mmHg, infiltrates over 50% of the lung fields, change in mental status, cyanosis, exhaustion or inability to complete a sentence, a rising PaCO₂ in a tachypnoeic patient, any child with SpO₂ below 90%, apnoea, inability to feed, lethargy, convulsions or a falling heart rate as they tire — and set the intubation decision point in advance rather than persisting with a failing non-invasive trial.

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