17th February 2025

Viral respiratory infections

Overview of viral respiratory infections

Viral respiratory tract infections tend to affect the upper respiratory regions and are often self limiting.  Due to their high transmissibility, viruses are likely candidates for respiratory pandemics, such as those seen in the COVID-19 pandemic. Detection is often via reverse transcriptase polymerase chain reaction (RT-PCR) testing or, alternatively, cultures grown from sputum or serum. Often, treatment is supportive.

Influenza

Influenza is the commonest cause of viral pneumonia in the immunocompetent and is especially prevalent during the flu season surrounding winter. In the UK, vaccination programmes aim to predict the likely strains that will have the most clinical impact in a given year. The influenza A virus is responsible for the majority of hospital illnesses; the H1N1 subtype has been involved in numerous epidemics including the Spanish flu and the 2009 swine flu outbreak. 

Diagnosis tends to be based on fever, myalgia, tachypnoea and wheeze. Often, superadded bacterial infections complicate the clinical picture. Diagnosis may be achieved through PCR or culture taken from swabs. Imaging often shows bilateral interstitial infiltrates unless complicated by a bacterial infection with focal consolidation. 

Treatment in the first instance is supportive, although intubation may be required in extremis. In the immunosuppressed or otherwise vulnerable presenting within the first 48 hours of symptoms, oseltamivir or other neuraminidase inhibitors reduce illness duration.

COVID-19

The COVID-19 pandemic was caused by the SARS-CoV-2 virus, which infiltrates the lungs through the angiotensin converting enzyme 2 receptor on type II alveolar cells in the lungs.

The classic symptoms include fever, anosmia and cough. A small proportion of people may develop a viral pneumonia which can deteriorate into severe respiratory dysfunction or multi-organ failure.

Diagnosis may be clinical or based on an RT-PCR test, although lateral flow immunochromatic assays may be used in a community setting. Blood tests typically show lymphopenia and may show thrombocytopenia. Chest X-ray may show bilateral consolidation and a CT typically shows ground glass opacities in a peripheral distribution. Pulmonary embolism risk is increased and CTPA should be considered.

Treatment is often supportive but dexamethasone is recommended for those requiring oxygen, as well as interleukin (IL)-6 inhibitors such as tocilizumab or sarilumab. In extreme circumstances, patients may require intubation or other organ support such as dialysis.

Cytomegalovirus (CMV)

Cytomegalovirus is a common viral pathogen in the immunocompromised. Transplantation and subsequent immunosuppression may cause reactivation of latent CMV infection. In addition, CMV-naive transplant recipients may be exposed to CMV from the donor organ.

Whilst CMV may cause viral pneumonia, it has various other manifestations, including hepatitis and retinitis. CMV PCR is the diagnostic mechanism of choice and viral load can be measured.

Treatment is with ganciclovir or valganciclovir first line; foscarnet may be used in resistant cases.

Other viral respiratory infections

Varicella

In the UK, most people are exposed to varicella in childhood (chickenpox), and pneumonia is rare. However, it is a more significant complication of infection in adults, particularly those who are pregnant. Treatment is with aciclovir.

Human metapneumovirus

Human metapneumovirus is a seasonal virus which usually causes a mild, self-limiting upper respiratory tract infection. Treatment is supportive, although antibiotics may be indicated with superadded bacterial infections.

Middle East respiratory syndrome (MERS)

This is caused by the MERS coronavirus and is found in the Middle East, especially Saudi Arabia. Due to the large risk to public health, isolation precautions and contact tracing are fundamental. Mortality is around 35%. Acute respiratory distress syndrome (ARDS) is the most serious complication and has reasonable prevalence. Diagnosis is via PCR and treatment is supportive.

Respiratory syncytial virus (RSV)

RSV is a common cause of bronchiolitis in children. In adults, it nearly always causes an indolent upper respiratory tract infection, but in the clinically vulnerable it can progress to pneumonia. Treatment is supportive only.

References

• National Institute for Health and Care Excellence. Guidance. Amantadine, oseltamivir and zanamivir for the treatment of influenza [Internet]. NICE. 2009 [accessed 23/08/22]. Available from: https://www.nice.org.uk/guidance/ta168/chapter/1-Guidance
• Ruuskanen O, Lahti E, Jennings LC, Murdoch DR. Viral pneumonia. Lancet (London, England) [Internet]. 2011;377(9773):1264–75 [accessed 23/08/22]. Available from: https://www.ncbi.nlm.nih.gov/pubmed/21435708/
• The RECOVERY Collaborative Group. Dexamethasone in Hospitalised Patients with Covid-19 — Preliminary Report. New England Journal of Medicine. 2020 Jul 17;384(8)
• Chapman S. Oxford handbook of respiratory medicine. Oxford, United Kingdom: Oxford University Press; 2014
• Kim AY, Gandhi RT. COVID-19: Management in hospitalised adults [Internet]. Hirsch MS, Bloom A, editors. UptoDate. 2022 [accessed 23/08/22]. Available from: https://www.uptodate.com/contents/covid-19-management-in-hospitalized-adults