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COVID-19 is the illness caused by the SARS-CoV-2 virus. Most people have a mild-to-moderate respiratory illness and recover within one to two weeks without needing specific treatment, but some — particularly older people and those with underlying health conditions — develop pneumonia or more severe disease needing hospital care and, occasionally, intensive care. Vaccination remains highly effective at preventing severe illness. This page covers the acute illness; for symptoms persisting beyond the initial infection see our Long COVID guide.
Definition
Acute coronavirus disease 2019 (COVID-19) is the illness caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a respiratory coronavirus first identified in 2019. Presentation ranges from asymptomatic infection through mild upper respiratory illness to severe viral pneumonia, acute respiratory distress syndrome (ARDS) and multi-organ involvement.1
Pathophysiology
The virus enters cells via the ACE2 receptor, present in high density in the respiratory epithelium, and triggers local inflammation and, in more severe cases, a disproportionate systemic inflammatory response. In the lungs this can progress to diffuse alveolar damage and ARDS.
SARS-CoV-2 also has a marked effect on the vascular endothelium. Endothelial injury and a pro-thrombotic state underlie the well-documented excess of pulmonary embolism, deep vein thrombosis and stroke in more severe infection, and distinguish COVID-19 pneumonia from most other viral pneumonias.1
Co-morbidities
Severe illness is strongly associated with older age and pre-existing conditions including COPD and other chronic lung disease, heart failure and cardiovascular disease, diabetes, obesity, chronic kidney disease and immunosuppression. These same conditions can be destabilised by acute infection independently of the direct effects of the virus — a COPD exacerbation or decompensated heart failure triggered by COVID-19 is treated as such, alongside the infection.
Prevalence
SARS-CoV-2 has caused several waves of infection worldwide since 2019 and continues to circulate, with periodic new variants. The large majority of cases in a well-vaccinated population are now mild, and hospitalisation and death rates have fallen substantially since the early pandemic, concentrated mainly in older, unvaccinated or medically vulnerable people.
Causes and risk factors
Infection is spread principally via respiratory droplets and aerosols from an infected person, with close, indoor and prolonged contact carrying the highest risk. Risk factors for severe disease include older age, being unvaccinated or under-vaccinated, pregnancy, immunosuppression and the co-morbidities above.
Symptoms
Common symptoms
Fever, cough, sore throat, fatigue, headache, muscle aches, and loss of taste or smell — the last far less prominent with more recent variants. Gastrointestinal symptoms are common in some variants, and in older people the presentation may be non-specific: falls, confusion or simply not being themselves.
Silent hypoxia
A distinctive feature of COVID-19 pneumonia is that oxygen saturation can fall well before the person feels particularly breathless. Pulse oximetry is therefore more reliable than symptom report in the at-risk, and a normal-sounding patient with a low saturation is a genuine emergency rather than a measurement error.
Recognising deterioration
Diagnosis
Why diagnosis matters
Confirming COVID-19 identifies who is eligible for early antiviral treatment — which must be started within days of symptom onset to work — and triggers the infection-control precautions that protect other patients. Both are time-limited opportunities.1
How is it diagnosed?
A PCR or rapid antigen test from a nasal or nasopharyngeal swab. Rapid antigen tests are less sensitive early in infection and in vaccinated people with low viral loads, so a single negative test in a symptomatic contact does not exclude infection.
Imaging
Chest X-ray or CT may show bilateral, peripheral ground-glass opacities in pneumonia. Imaging is not needed in mild illness and adds little to diagnosis; its value is in assessing severity and identifying complications such as pulmonary embolism.
Assessing severity
Pulse oximetry at rest and, where appropriate, on exertion is the key bedside measure. Blood tests — inflammatory markers, D-dimer, renal function — help gauge severity and clotting risk in those unwell enough for hospital assessment.1
Investigations for related conditions
A rising D-dimer with disproportionate hypoxia prompts investigation for pulmonary embolism, and new chest pain or arrhythmia prompts cardiac assessment, given the recognised association with myocarditis.
Management
Management and goals
The goals are to prevent progression in those at risk, support oxygenation where the lungs fail, prevent thrombotic and immobility-related complications, and return the person to their previous function.1
Managing at home
Most people manage with rest, fluids and symptomatic treatment, isolating while infectious per current public health guidance. Those at higher risk of severe disease may be eligible for early oral antiviral treatment, which substantially reduced hospitalisation and death in unvaccinated high-risk adults when started within five days of symptom onset.2 Eligibility criteria change over time and are worth checking against current national guidance rather than memory.
In hospital
Corticosteroids reduced mortality in patients requiring supplemental oxygen or ventilation, and are standard for that group — but showed no benefit, and a possible signal of harm, in those not requiring oxygen.3 Interleukin-6 blockade with tocilizumab improves survival in hospitalised patients with hypoxia and systemic inflammation, added to corticosteroids.4 Thromboprophylaxis is routine given the pro-thrombotic state.
Oxygen and respiratory support
High-flow nasal oxygen reduced the need for invasive mechanical ventilation and shortened recovery compared with conventional oxygen in severe COVID-19.5 Awake prone positioning in patients on high-flow oxygen reduced treatment failure and the need for intubation, and is a low-cost intervention frequently delivered and supervised by physiotherapy.6 The WHO living guideline now carries a conditional recommendation for it — added in the seventh version (18 August 2023) for severely ill hospitalised patients requiring supplemental oxygen, including high-flow nasal oxygen, or non-invasive ventilation, on moderate-to-low certainty evidence.1 That matters for scope: it moves awake proning from trial evidence to recommended care, in an intervention physiotherapists typically deliver. In intubated patients with moderate-to-severe ARDS, prone positioning has an established mortality benefit.7
Vaccination
Vaccination remains the most effective way to prevent severe illness, hospitalisation and death, and is recommended on an ongoing booster schedule for eligible groups. Its effect on preventing infection wanes considerably faster than its effect on preventing severe disease — which is why breakthrough infection in a vaccinated person is not evidence of failure.
Identifying deterioration
Falling oxygen saturation, rising respiratory rate, new confusion or a sudden increase in breathlessness — particularly in the second week — indicate progression. Exertional desaturation may appear before resting saturation falls.
Action plan
- Test early if symptomatic and at higher risk — antiviral eligibility is time-limited.
- Rest, hydrate and monitor. If you have an oximeter, record saturation at the same times each day.
- Seek urgent care for breathlessness at rest, chest pain, confusion, or saturation below your advised threshold.
- Keep moving gently at home; complete bed rest is not advised unless you are too unwell to be up.
- Return to activity gradually — see below — rather than resuming full training or workload at once.
- Seek review if symptoms are not settling as expected, or new symptoms appear after apparent recovery.
Medications
Antivirals
Oral antivirals such as nirmatrelvir/ritonavir are used in higher-risk outpatients within days of onset.2 Nirmatrelvir/ritonavir has clinically important interactions with many common medicines, including some statins and anticoagulants, so the full medication list is reviewed before prescribing.
Corticosteroids
Dexamethasone is given to those requiring oxygen, not to those who are not — one of the clearest examples in the pandemic of a treatment whose benefit depends entirely on disease severity.3
Immunomodulators
Tocilizumab and similar agents are added in hospitalised patients with hypoxia and marked inflammation.4
Anticoagulation
Prophylactic-dose anticoagulation is standard for hospitalised patients; therapeutic dosing is reserved for confirmed thrombosis or specific indications.
What does not help
Antibiotics do not treat a viral illness and are reserved for proven or strongly suspected bacterial co-infection, which is uncommon. Several widely promoted agents were tested in large randomised trials and found ineffective; the trials that established what works also established what does not, and both results matter.1
Multi-system manifestations
Cardiovascular
Myocarditis, arrhythmia, acute coronary events and a markedly raised risk of venous thromboembolism are all recognised. New chest pain, palpitations or exertional intolerance during or shortly after infection warrants cardiac assessment before returning to intensive exercise.
Neurological
Anosmia, headache, delirium — particularly in older inpatients — stroke, and Guillain–Barré syndrome have all been described. Delirium is frequently the presenting feature in frail older people.
Kidneys
Acute kidney injury is common in severe disease, multifactorial, and an independent predictor of poor outcome.
Metabolic and endocrine
Hyperglycaemia is common during acute illness, both from corticosteroid treatment and from the infection itself, and new-onset diabetes has been reported after infection.
Muscle and physical function
Prolonged critical illness produces ICU-acquired weakness, and even non-critical hospitalised patients lose substantial muscle mass and function. This, rather than residual lung damage, is often the dominant limitation at discharge — which makes it a physiotherapy problem first.
Living with COVID-19
Returning to activity and exercise
A structured, gradual return — increasing one variable at a time and allowing a day to judge the response — reduces the risk of a difficult recovery. Return to sport after any illness with cardiac symptoms is deferred until cardiac assessment is complete.
Pacing rather than pushing
Where fatigue is prominent, symptom-titrated progression works better than fixed weekly increments. Repeated boom-and-bust cycles are the pattern most likely to prolong recovery, and recognising them early is the useful clinical skill.
Protecting others
Isolation while infectious, ventilation, and mask use around vulnerable contacts remain the practical measures, particularly for people living or working with immunosuppressed or elderly household members.
When symptoms persist
Symptoms continuing beyond the expected recovery window — fatigue, breathlessness, cognitive difficulty, exertional intolerance — are addressed in our Long COVID guide, where the management principles differ importantly from those for acute illness.
Prognosis
The great majority of people, especially those vaccinated, recover fully within one to two weeks. Older people, those with significant co-morbidities and the unvaccinated remain at higher risk of severe illness, hospitalisation and, uncommonly, death. A minority develop persisting symptoms beyond the acute phase, and those who required intensive care face a recovery measured in months and dominated by weakness and deconditioning rather than by lung damage.
Role of the physiotherapist
Physiotherapy in acute COVID-19 is largely about mobility, positioning and oxygenation rather than sputum clearance — most patients have a dry, non-productive cough, and routine airway-clearance techniques are not indicated unless there is a secretion problem. National clinical practice recommendations set out this scope explicitly, including the infection-control considerations around aerosol-generating procedures.8
- In hospital — awake prone positioning, positioning to optimise ventilation–perfusion matching, early mobilisation and oxygen-weaning support.6
- In intensive care — early physical and occupational therapy improves return to independent function in mechanically ventilated patients and reduces delirium duration.9
- After discharge — graded reconditioning for the weakness and deconditioning that dominate recovery, with monitoring of breathlessness, heart rate and oxygen saturation during activity.
- Persisting symptoms — outpatient pulmonary rehabilitation improves exercise capacity, functional status, breathlessness, fatigue and quality of life in people with persisting post-COVID symptoms.10
Physiotherapy red flags — stop and escalate: exertional desaturation, new chest pain or palpitations, resting breathlessness, new confusion, or symptoms that consistently worsen for more than 24 hours after activity.
Part 1 · References
- World Health Organization. Clinical management of COVID-19: living guideline, seventh version. Geneva: WHO; 18 August 2023. Available at: app.magicapp.org. Living guideline — cite the version, as recommendations are added between editions.
- Hammond J, Leister-Tebbe H, Gardner A, et al. Oral nirmatrelvir for high-risk, nonhospitalized adults with Covid-19. N Engl J Med 2022;386(15):1397–1408.
- RECOVERY Collaborative Group. Dexamethasone in hospitalized patients with Covid-19. N Engl J Med 2021;384(8):693–704.
- RECOVERY Collaborative Group. Tocilizumab in patients admitted to hospital with COVID-19: a randomised, controlled, open-label, platform trial. Lancet 2021;397(10285):1637–1645.
- Ospina-Tascón GA, Calderón-Tapia LE, García AF, et al. Effect of high-flow oxygen therapy vs conventional oxygen therapy on invasive mechanical ventilation and clinical recovery in patients with severe COVID-19: a randomized clinical trial. JAMA 2021;326(21):2161–2171.
- Ehrmann S, Li J, Ibarra-Estrada M, et al. Awake prone positioning for COVID-19 acute hypoxaemic respiratory failure: a randomised, controlled, multinational, open-label meta-trial. Lancet Respir Med 2021;9(12):1387–1395.
- Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome (PROSEVA). N Engl J Med 2013;368(23):2159–2168.
- Thomas P, Baldwin C, Bissett B, et al. Physiotherapy management for COVID-19 in the acute hospital setting: clinical practice recommendations. J Physiother 2020;66(2):73–82.
- Schweickert WD, Pohlman MC, Pohlman AS, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet 2009;373(9678):1874–1882.
- Nopp S, Moik F, Klok FA, et al. Outpatient pulmonary rehabilitation in patients with long COVID improves exercise capacity, functional status, dyspnea, fatigue, and quality of life. Respiration 2022;101(6):593–601.
References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.
More than one of our services applies here, and which combination suits you depends on what your assessment shows.
Clinical evidence
Part 1 covers the same condition without the technical detail. What follows is the evidence base behind it, written for clinicians — the literature, the reasoning and the gaps.
For clinicians: this summary supports clinical reasoning and is not a protocol. Check current guidelines and local policy before applying it, and read it alongside the key references and guidelines directory.
Framing. Acute COVID-19 in a vaccinated, largely immune population is a different disease from 2020: fewer hospitalisations, less severe hypoxaemia and far less ICU-level care, but the same underlying respiratory pathology when it is severe. The evidence base that matters to physiotherapists is unusual in that its central finding is restraint — the pneumonitis is not a secretion-retention problem, so routine airway clearance has no role in the typical patient, while positioning, mobility and oxygenation strategies do.1,2
Acute medical management
- Dexamethasone reduced 28-day mortality in patients requiring oxygen or ventilation in RECOVERY, with no benefit (and possible harm) in those not requiring oxygen — the first therapy shown to save lives.3
- Interleukin-6 receptor blockade (tocilizumab) further improved survival in hospitalised patients with hypoxia and systemic inflammation.4
- Nirmatrelvir–ritonavir reduced progression to severe disease in high-risk unvaccinated outpatients in EPIC-HR; benefit in vaccinated, previously infected populations is smaller and concentrated in the elderly and immunosuppressed.5
- High-flow nasal oxygen reduced escalation to invasive ventilation and shortened recovery compared with conventional oxygen in acute hypoxaemic COVID-19.6
Positioning, mobility and physiotherapy
- Awake prone positioning reduced treatment failure and the need for intubation in patients on high-flow oxygen in a randomised meta-trial — the single most physiotherapy-relevant intervention of the pandemic, with effect dependent on daily duration achieved.7
- Prone positioning in intubated ARDS reduced mortality in PROSEVA and remains standard care where the criteria are met.8
- Physiotherapy practice recommendations developed early in the pandemic and still applicable: airway clearance only for demonstrable secretion retention or comorbid suppurative disease, careful aerosol-generating-procedure risk assessment, and prioritisation of mobilisation and rehabilitation.1
- Early rehabilitation of the critically ill improves functional outcomes and reduces ICU-acquired weakness; the same principles apply here, moderated by profound exertional desaturation in the acute phase.9
- Post-hospital rehabilitation improves exercise capacity, breathlessness and quality of life in survivors, and referral should be the default at discharge.10
Physiotherapy implications
- Do not treat a dry chest. Percussion, vibration and forced expiratory techniques are not indicated in uncomplicated COVID-19 pneumonitis and consume PPE, staff time and patient reserve.1
- Own the positioning plan: teach, time and document awake proning and side-lying cycles, aiming for the longest tolerated daily duration with a clear plan for the patient who cannot self-turn.7
- Monitor exertional desaturation closely during early mobilisation; recovery time after activity is more informative than the nadir alone, and progression should be conservative in the first days.
- Treat the deconditioning and the delirium — both are the dominant functional problems in survivors, and both respond to structured daily mobility rather than respiratory technique.9
- Escalate rising oxygen requirement, respiratory rate above 30, silent hypoxaemia, exhaustion with a falling respiratory rate, or new chest pain (consider pulmonary embolism — thrombotic risk is raised in acute COVID-19).
- Screen at discharge for persistent breathlessness, fatigue, post-exertional symptom exacerbation and breathing pattern disorder, and route to the appropriate pathway rather than a generic exercise programme.
Clinical reasoning
- Ask whether the problem is oxygenation (shunt — treat with positioning and oxygen), ventilation (fatigue — escalate), or secretions (rare — treat only if present).
- Marked desaturation with modest symptoms is characteristic and should not be dismissed because the patient looks well.
- A secondary bacterial pneumonia, superimposed heart failure or pulmonary embolism explains many sudden deteriorations attributed to the virus itself.
- In the recovering patient, persistent limitation out of proportion to imaging suggests deconditioning, dysfunctional breathing or post-COVID syndrome rather than ongoing lung injury.
Evidence gaps
- Optimal duration, frequency and patient selection for awake prone positioning remain undefined despite the positive trial signal.7
- Almost all acute physiotherapy evidence is consensus-based rather than randomised.1
- Whether findings from earlier variants and unvaccinated cohorts transfer to current, largely immune populations is uncertain.
- The optimal timing, intensity and content of rehabilitation after severe COVID-19 — particularly where post-exertional symptom exacerbation is present — is still being defined.10
References for the clinical evidence summary
- Thomas P, Baldwin C, Bissett B, et al. Physiotherapy management for COVID-19 in the acute hospital setting: clinical practice recommendations. J Physiother 2020;66(2):73–82.
- World Health Organization. Clinical management of COVID-19: living guideline. Geneva: WHO; 2023.
- RECOVERY Collaborative Group. Dexamethasone in hospitalized patients with Covid-19. N Engl J Med 2021;384(8):693–704.
- RECOVERY Collaborative Group. Tocilizumab in patients admitted to hospital with COVID-19: a randomised, controlled, open-label, platform trial. Lancet 2021;397(10285):1637–1645.
- Hammond J, Leister-Tebbe H, Gardner A, et al. Oral nirmatrelvir for high-risk, nonhospitalized adults with Covid-19. N Engl J Med 2022;386(15):1397–1408.
- Ospina-Tascón GA, Calderón-Tapia LE, García AF, et al. Effect of high-flow oxygen therapy vs conventional oxygen therapy on invasive mechanical ventilation and clinical recovery in patients with severe COVID-19: a randomized clinical trial. JAMA 2021;326(21):2161–2171.
- Ehrmann S, Li J, Ibarra-Estrada M, et al. Awake prone positioning for COVID-19 acute hypoxaemic respiratory failure: a randomised, controlled, multinational, open-label meta-trial. Lancet Respir Med 2021;9(12):1387–1395.
- Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome (PROSEVA). N Engl J Med 2013;368(23):2159–2168.
- Schweickert WD, Pohlman MC, Pohlman AS, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet 2009;373(9678):1874–1882.
- Nopp S, Moik F, Klok FA, et al. Outpatient pulmonary rehabilitation in patients with long COVID improves exercise capacity, functional status, dyspnea, fatigue, and quality of life. Respiration 2022;101(6):593–601.
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