17th February 2025

Respiratory Infections

Bacterial respiratory infections

Overview of bacterial respiratory infections

Bacterial pathogens constitute a majority of respiratory infections that require medical intervention and treatment. The different bacterial pathogens often result in specific clinical courses. 

The vast majority of community-acquired pneumonia is caused by Streptococcus pneumoniae and Haemophilus influenzae. Atypical pneumonia is caused by pathogens that may be harder to detect, such as Legionella, Mycoplasma or Chlamydia, and are associated with specific causes. Hospital-acquired pneumonia is defined as pneumonia starting from 72 hours after admission to hospital and is very often bacterial. Hospital-acquired pneumonia is associated with a worse outcome than community-acquired pneumonia. Ventilator-acquired pneumonia is common in patients who are on ventilators for longer than 72 hours; this carries a poor prognosis.

Pathogens

Key respiratory bacterial pathogens

Strep. pneumoniae is a Gram-positive coccus which accounts for the majority of community-acquired pneumonia; around 60%. Infection is particularly severe in asplenic patients and carries a high rate of mortality, necessitating vaccination and prophylactic phenoxymethylpenicillin. Strep. pneumoniae exists as a commensal organism in the nasopharynx in up to 60% of people.

H. influenzae is a Gram-negative bacillus. H. influenzae type B may cause epiglottitis, especially in the unvaccinated. It is a common causative organism in infective exacerbations of COPD. Its main complications can include meningitis and pneumonia.

Staphylococcus aureus  is a Gram-positive coccus. It is highly associated with being a superadded bacterial infection following influenza and can carry a high mortality rate. Pneumonia may also occur following septicaemia in intravenous drug misuse or hospital patients with indwelling lines. The production of the Panton-Valentine leukocidin (PVL) toxin can cause tissue necrosis, cavitation and, rarely, pneumothorax.

Klebsiella pneumoniae is a Gram-negative organism which is now highly drug resistant in the United Kingdom. It may result in an intractable pneumonic infection due to its high resistance to antibiotics. It is especially seen in patients who have impaired resistance to infections including the homeless, the malnourished and those with alcohol misuse. It may also be seen in patients with underlying lung disease.

Pseudomonas aeruginosa is a Gram-negative bacillus common in hospital-acquired pneumonia, aspiration pneumonia and patients who have required endotracheal ventilation. It is drug resistant and requires an antipseudomonal antibiotic such as piperacillin with tazobactam.

Atypical pneumonia

Mycoplasma pneumoniae causes a characteristic flu-like prodrome consisting of headaches, muscle aches and fatigue before progressing into a dry cough and shortness of breath. One may see bilateral peribronchial infiltrates on chest X-ray. It is rarely life threatening. Complications can include a cold, autoimmune haemolytic anaemia, erythema multiforme, transverse myelitis and rarely lymphocytic meningoencephalitis.

Chlamydophilia pscittaci is a zoonotic infection arising from contaminated droplets, particularly from birds, with the main complications including severe pneumonia, fevers and delirium.

Legionella pneumophila is a Gram-negative bacillus found in contaminated water. For this reason, it is especially associated with unclean air conditioners, showers and water storage tanks. Alongside severe pneumonia, it may cause abdominal pain, confusion, hyponatraemia and transaminitis. A urinary antigen test may confirm the diagnosis although direct fluorescent antibody staining on a bronchoalveolar lavage sample is more sensitive.

Coxiella burnetii, the causative agent of Q fever, is another zoonotic infection often obtained from domesticated animals, especially sheep, cattle or goats. It typically causes flu-like symptoms but can progress to an atypical pneumonia with severe respiratory distress. Rarely, hepatitis can be a complication.

Other respiratory bacterial pathogens

Nocardia are Gram-positive aerobic bacilli found in soil. Whilst the lung is the most common site of infection, dissemination can occur to the CNS, causing abscesses and meningitis or alternatively to the skin and subcutaneous tissues causing soft tissue abscesses. It may also cause endocarditis. Direct smears of abscesses are often positive, whereas cultures seldom are. Extended antibiotic courses and abscess drainage are standard treatments.

Leptospirosis is caused by the bacterium Leptospira. Whilst being more known for causing icterohaemorrhagic fever, it can also cause a diffuse alveolar haemorrhage and subsequent respiratory decompensation through this mechanism. It is particularly associated with sewers and rodents.

Grading pneumonia

The CURB-65 score is a screening tool used to assess the severity of pneumonia. It uses the following criteria:

• C – Confusion
• U – Urea > 7.0
• R – Respiratory rate > 30/minute
• B – Systolic blood pressure < 90 or diastolic blood pressure < 60 mgHg
• 65 – Age 65 or older 

Scores ≥3 are at highest risk with a mortality of  >15% and require hospital admission and consideration of ICU.

Investigating pneumonia

Patients with bacterial pneumonia often present with a productive cough, shortness of breath and fever. They may be tachypnoeic with localised crackles with dullness to percussion on auscultation, reflecting underlying consolidation. Other symptoms or signs typical of any severe infection, such as tachycardia and reduced urine output, may also be present.

Initial investigations

A full history, examination, bloods and a chest X-ray would be expected as a minimum. Blood cultures and sputum cultures may be useful, especially for atypical organisms. Urine samples may be used to look for pneumococcal or Legionella antigen; PCR is necessary for confirmation of Mycoplasma.

If unable to achieve samples, a bronchoalveolar lavage may help. If there is an effusion, a pleural aspirate may offer a diagnosis. A pH <7.2 is diagnostic of a complicated parapneumonic effusion. If the patient requires a pleural tap, the triangle of safety offers borders which minimise the risk of iatrogenic harm: lateral border of the pectoralis major, lateral border of the latissimus dorsi and line of the fifth intercostal space.

Further investigations

A CT thorax can be used in severe cases or to assess for cavitation or abscess. A pulmonary abscess could be from septic emboli from endocarditis and an echocardiogram would be recommended. 

Recurrent or atypical bacterial pneumonia should prompt consideration of an underlying immunodeficiency such as HIV or cancer, including myeloma. Alternatively, recurrent bacterial infections in a young person with worsening respiratory function may prompt testing for cystic fibrosis or alpha-1 antitrypsin deficiency-related COPD.

On discharge, patients should be followed up with a 6 week post-discharge chest X-ray to assess for resolution and possible underlying causes of pneumonia, including malignancy.

Managing bacterial pneumonia

Management of pneumonia includes oxygen therapy and IV crystalloid fluids if the patient is septic. Chest physiotherapy may be used to increase expectoration and alveolar recruitment. 

Non-invasive ventilation (NIV) is not typically indicated in pneumonia but may be undertaken with expert supervision on a case-specific basis. Worsening oxygenation despite appropriate therapy will necessitate intubation and ventilation. The positive end-expiratory pressure (PEEP) from mechanical ventilation can increase oxygenation by increasing alveolar recruitment.  

Antibiotics will be required to treat pneumonia, with IV administration recommended for a CURB-65 score ≥2. Aspiration pneumonia requires an antibiotic with Pseudomonas cover. Atypical pneumonias should be covered with a fluoroquinolone or macrolide antibiotic. In cases of recurrent lower respiratory tract infections due to COPD, a prophylactic antibiotic such as azithromycin may be indicated.

Complications of bacterial pneumonia

In severe cases of pneumonia a septic picture may emerge, which can include an acute kidney injury, disseminated intravascular coagulation and a high risk of mortality.

Other complications include syndrome of inappropriate antidiuretic hormone, pulmonary abscesses, parapneumonic effusions and empyema. Rarely, often in vulnerable patients prone to self neglect, a long-standing empyema may dissect from the pleural space and invade through the chest wall, which is described as empyema necessitans.

References

• Chapman S. Oxford handbook of respiratory medicine. Oxford, United Kingdom: Oxford University Press; 2014
• H. Ticona J, M. Zaccone V, M. McFarlane I. Community-Acquired Pneumonia: A Focused Review. American Journal of Medical Case Reports. 2020 Nov 4;9(1):45–52
• Noviello S, Huang D. The Basics and the Advancements in Diagnosis of Bacterial Lower Respiratory Tract Infections. Diagnostics. 2019 Apr 3;9(2):37
• Ramirez JA. Overview of community-acquired pneumonia in adults [Internet]. File TM, Bond S, editors. UpToDate. 2022 [accessed 13/08/2022]. Available from: https://www.uptodate.com/contents/overview-of-community-acquired-pneumonia-in-adults
• Cunha BA. The atypical pneumonias: clinical diagnosis and importance. Clinical Microbiology and Infection. 2006;12(3):12–24
• National Institute for Health and Care Excellence. Pneumonia (hospital-acquired): antimicrobial prescribing [Internet]. NICE. 2019 [accessed 13/08/2022]. Available from: https://www.nice.org.uk/guidance/ng139
• Davies HE, Davies RJO, Davies CWH. Management of pleural infection in adults: British Thoracic Society pleural disease guideline 2010. Thorax [Internet][accessed 18/08/2022]. 2010 Aug 1;65(Suppl 2):ii41–53. Available from: https://thorax.bmj.com/content/65/Suppl_2/ii41#T1
• Kinnear W. Non-invasive ventilation in acute respiratory failure. Thorax. 2002 Mar 1;57(3):192–211
• Najib Rahman, Hunt I, Fergus Gleeson, Maskell N. ABC of pleural diseases. Hoboken, New Jersey: Wiley Blackwell; 2018
• Bourke SJ, Burns GP. Lecture notes. Respiratory medicine. Chichester, West Sussex; Hoboken, Nj: John Wiley & Sons, Ltd; 2015

Fungal respiratory infections

Overview of fungal respiratory infections

Fungal diseases of the lung are mostly associated with the immunosuppressed or those with complications from tuberculosis. History is fundamental due to the subset of patients most susceptible.

In the laboratory, beta-d-glucan is a useful fungal-specific marker which may aid in diagnosis.

Pneumocystis pneumonia (PCP)

PCP is an opportunistic fungal infection of the lung which causes an idiosyncratic pneumonia. It is strongly associated with HIV but may also be seen in immunosuppressed transplant patients, those on corticosteroids, following chemotherapy or in patients with cancer.

Classically, the infection causes a cough with severe desaturation on exertion.

Chest X-ray often shows bilateral hilar infiltrates; however, chest examination is often normal. Microscopy is the diagnostic tool in PCP, with bronchoalveolar lavage being the gold standard.

First-line treatment is co-trimoxazole (trimethoprim and sulfamethoxazole). In patients at particular risk of PCP, co-trimoxazole may be given prophylactically. Continuous positive airway pressure (CPAP) may be used to assist with oxygenation in PCP and intubation may be needed. For patients with an oxygen requirement, corticosteroids should be given.

Histoplasmosis

Histoplasma is a fungus found in animal droppings in the Midwest and South-East USA, with particular prevalence around the Mississippi River. The disease is also prevalent in Mexico and Central America. 

In immunocompetent individuals, the disease is often asymptomatic, although 1-3 weeks after acquisition, patients may develop a self-limiting flu-like illness with bilateral alveolar shadowing and hilar/mediastinal lymphadenopathy on chest X-ray. Some cases may turn into chronic, cavitating disease. Disseminated disease can occur in the immunosuppressed. Adrenal insufficiency is a rare, life-threatening complication.

Gold-standard diagnosis involves Histoplasma seen either on microscopy or histopathology from biopsied tissue. Alternatively, diagnosis can be obtained via antigen testing. Oral itraconazole is the treatment.

Aspergillus

Aspergillus moulds, especially Aspergillus fumigatus, can produce a variety of respiratory diseases.

Allergic bronchopulmonary aspergillosis (ABPA)

Asthma precipitated by Aspergillus and ABPA are IgE- and IgG-mediated reactions which are responsive to steroids. Signs and symptoms are typical of asthma and include reduced exercise tolerance and wheeze.

Patients with ABPA have a chronic inflammatory IgE and IgG response to Aspergillus, which causes damage to bronchi and eventually bronchiectasis. Diagnosis is mainly based on a history of asthma (particularly with recurrent exacerbations), IgG precipitins to Aspergillus, central bronchiectasis and a positive skin prick test. Patients benefit from itraconazole alongside steroids and conventional asthma treatment. 

Invasive aspergillosis 

This is when Aspergillus hyphae invade body tissue. Invasive aspergillosis occurs nearly exclusively in cases of immunosuppression. Isolating Aspergillus hyphae from the respiratory tract via sputum or a bronchoalveolar lavage provides a diagnosis.

Invasive disease can cause fever, haemoptysis and dyspnoea when afflicting the lungs; other pathologies, such as endocarditis, depend on the site of dissemination. The lungs are the most common mechanism of entry to the body.

Raised circulating levels of galactomannan, a component of the Aspergillus cell wall, provides evidence of aspergillosis. Management is with a prolonged course of an IV antifungal.

Aspergilloma

Aspergillomas are balls of fungal hyphae that exist within a cavity in the lung, usually secondary to previous tuberculosis infection. Haemoptysis is the most common symptom, but many aspergillomas are asymptomatic. CT thorax may show the halo sign.

Treatment is dependent on symptoms; surgery or antifungals may be required.

Candidal pneumonia

Candidal pneumonia, caused by Candida, may occur in the immunosuppressed, especially in transplant patients. Due to the neutropenia required for bone marrow transplantation, these patients are particularly susceptible. Pulmonary involvement with candidal infection is non specific but carries a high mortality and the patient may be severely unwell.

A T2 magnetic resonance (T2MR) assay will be positive but a transbronchial or surgical lung biopsy is required for a definitive diagnosis. Treatment is with an antifungal such as fluconazole or amphotericin B.

Cryptococcus

Cryptococcal lung disease, caused by Cryptococcus neoformans, is rare but possible in the immunosuppressed. Pulmonary involvement will necessitate a CT head and lumbar puncture due to the strong association with CNS involvement. Serum cryptococcal antigen will help make a diagnosis. Treatment is with several weeks of IV antifungals.

Blastomycosis

Blastomycosis is caused by Blastomyces dermatitidis, a fungus found in contaminated soil mostly in the United States but also in South Asia and the Middle East. It is uncommon and mostly asymptomatic but can cause a severe pneumonia with ARDS as a rare but serious complication. Treatment is with itraconazole.

References

• Tasaka S. Recent Advances in the Diagnosis and Management of Pneumocystis Pneumonia. Tuberculosis and Respiratory Diseases. 2020;83
• Linder KA, Kauffman CA. Histoplasmosis: Epidemiology, Diagnosis, and Clinical Manifestations. Current Fungal Infection Reports. 2019 May 7;13(3):120–8
• Chapman S. Oxford handbook of respiratory medicine. Oxford, United Kingdom: Oxford University Press; 2014
• Akuthota P. Clinical manifestations and diagnosis of allergic bronchopulmonary aspergillosis [Internet]. Kauffman CA, Barnes PJ, Finlay G, editors. UptoDate. 2022 [cited 2022 Apr 27]. Available from: https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-allergic-bronchopulmonary-aspergillosis
• National Institute for Health and Care Excellence. Antifungals, systemic use [Internet] [accessed 17/08/2022]. NICE. Available from: https://bnf.nice.org.uk/treatment-summary/antifungals-systemic-use.html
• McBride JA, Gauthier GM, Klein BS. Clinical Manifestations and Treatment of Blastomycosis. Clinics in Chest Medicine. 2017 Sep;38(3):435–49

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

Mycobacterial respiratory infections

Mycobacterium tuberculosis (TB)

Symptoms of TB

TB is a multi-organ infection caused by the bacterium Mycobacterium tuberculosis. Whilst the key manifestations tend to be pulmonary, systems such as the CNS, GI tract and musculoskeletal system may also be involved.

The main symptoms of pulmonary TB include weight loss, fevers, cough, fatigue and haemoptysis. Due to this array of symptoms, malignancy will also be high on the list of differentials.

Other symptoms such as confusion, joint or bone pain or abdominal pain may be evidence of extrapulmonary involvement; this is more prevalent in the immunosuppressed. Symptoms of extrapulmonary tuberculosis are dependent on the systems involved. Tuberculomas, which are firm masses formed in tuberculosis, may exert mass effects in areas where they arise. A spinal tuberculoma may produce a spinal deformity, alongside pain and if not treated, sensory and motor dysfunctions. Pericardial tuberculosis can result in constrictive pericarditis, which may be fatal.  Tuberculosis of the central nervous system can present as TB meningitis with the usual symptoms of pain, fever, confusion and neck stiffness.

The rates of tuberculosis in the UK tend to be highest in cities with high immigrant populations, such as London, but it is also more common in immunosuppressed or homeless populations.

Investigations in TB

Aside from history taking and examination, primary investigations for TB include a chest radiograph and three respiratory cultures. Respiratory cultures should be early morning samples from a deep cough. Zeihl-Neelsen staining (an acid-fast bacilli test) is used but can be falsely negative, particularly with HIV. Bronchoalveolar lavage can be used to obtain samples in non-productive patients or if cultures are negative with high clinical suspicion.

In HIV-positive patients, rapid diagnostic nucleic amplification tests can be used to assess for active TB infection. This may be used for rapid diagnosis but cannot be used to exclude TB.

A chest X-ray may show lymphadenopathy, especially around the hilar regions, but it may also look normal. In some cases of disseminated tuberculosis, a chest X-ray may show miliary TB, where there are diffusely spread nodules throughout the chest. CT chest may show cavitation, which can become infiltrated with fungal diseases such as an aspergilloma.

A positive Mantoux test or positive interferon-gamma release assay (IGRA) can be used to demonstrate latent TB. An interferon-gamma release assay cannot distinguish between latent or active TB. 

Extrapulmonary TB is investigated according to the site of suspected involvement. CNS involvement warrants a CT head or spine and lumbar puncture to assess for cavitation, meningitis or tuberculoma. Lymphadenopathy may be assessed with a fine needle tissue biopsy. Pericardial TB warrants an echocardiogram and possible pericardiocentesis with specimen sampling. Joint involvement requires an ultrasound scan and aspiration of joint fluid.

Patients starting anti-TNF-alpha treatment, e.g. infliximab, should be tested for TB prior to commencing treatment.

Treatment of TB

The standard treatment regimen for active TB in the UK is 6 months of rifampicin and isoniazid, with the addition of pyrazinamide and ethambutol for the first 2 months. Pyridoxine (vitamin B6) should be prescribed alongside isoniazid for the entire duration of its usage to minimise the risk of neuropathy.

For CNS involvement, TB treatment should consist of 12 months of rifampicin and isoniazid (with pyridoxine), with the first 2 months supplemented by pyrazinamide and ethambutol. Patients with CNS involvement should be offered 4-8 weeks of corticosteroids at the start of treatment.

Multidrug-resistant TB will require extended courses of antibiotics based on resistance patterns. 

The Bacillus Calmette-Guérin (BCG) vaccine has resulted in substantially reduced mortality from TB worldwide and is still recommended in countries of high prevalence, although currently, in the UK, it is only offered to high-risk populations.

Common side effects of the TB medications are as follows:

• Rifampicin: potent cytochrome P450 inducer; red/orange discolouration of bodily fluids; hepatotoxicity
• Isoniazid: peripheral nerve damage
• Pyrazinamide: gout
• Ethambutol: optic neuritis

Non-tuberculous mycobacteria

Non-tuberculous mycobacteria are organisms that mostly affect the immunosuppressed or those with chronic lung disease.

Most prevalent is a Mycobacterium avium complex (MAC) syndrome, caused by an array of non-tuberculous mycobacterium which conolonsie the respiratory tract of humans but are not usually pathogenic in the immunocompetent. There is an occupational risk for those who work with contaminated water or certain animals. Rarely, chronic cough suppression can lead to non-tuberculosis mycobacterium infiltration, a phenomenon typically seen in elderly women known as Lady Windermere syndrome.

Symptoms are often non specific but may include a chronic productive cough, anorexia and fatigue. Mycobacterial treatment medications such as rifampicin may be employed if the infection is causing sufficient symptoms.

Notable species include:

• Mycobacterium marinum: may cause pulmonary disease and is related to working with fish
• M. Leprae: one of the causative organisms of leprosy
• M. Bovis: causes tuberculosis in cattle but can cause a tuberculous-like disease in humans
• M. Africanum: most common in West Africa; can cause a tuberculous-like pulmonary disease

References

• National Institute for Health and Care Excellence. Tuberculosis [Internet]. NICE. 2016 [accessed 23/08/22]. Available from: https://www.nice.org.uk/guidance/ng33/chapter/recommendations#active-tb
• National Institute for Health and Care Excellence. Clinical Knowledge Summaries: Tuberculosis [Internet]. NICE. 2019 [accessed 23/08/22]. Available from: https://cks.nice.org.uk/topics/tuberculosis/
• Tanoue LT. BTS recommendations for assessing risk and for managing Mycobacterium tuberculosis infection and disease in patients due to start anti-TNF-α Treatment. Yearbook of Pulmonary Disease. 2007 Jan;2007:345–8
• Chapman S. Oxford handbook of respiratory medicine. Oxford, United Kingdom: Oxford University Press; 2014
• Smith I. Mycobacterium tuberculosis Pathogenesis and Molecular Determinants of Virulence. Clinical Microbiology Reviews [Internet]. 2003 Jul 1;16(3):463–96 [accessed 23/08/22]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC164219/

Parasitic respiratory infections

Overview of parasitic respiratory infections

Parasitic lung infections are rare in the UK and will mostly be encountered in the returning traveller and the immunosuppressed. Whilst there is a risk of direct infection and subsequent manifestation of disease, hypersensitivity reactions are generally the main presentation. 

The distribution of parasitic infections is likely to change with a changing global climate. 

Schistosomiasis

Schistosomiasis is a helminthic infection caused by one of five types of schistosome. The schistosomes are found in infested water and often use snails as a vector. Areas of particular incidence are East Asia, central Africa and, less commonly, the Mediterranean and Caribbean.

Pulmonary schistosomiasis is likely to present as wheeze, restrictive pulmonary compromise and chest X-ray infiltrates in the acute setting. It may be treated with praziquantel and is usually self-limiting.

Chronic infection may cause granulomatous reactions leading to pulmonary hypertension and pulmonary fibrosis.

Pulmonary hydatid disease

Pulmonary hydatid disease is caused by ingestion of parasitic eggs, with dogs, goats and sheep the most common vector for the adult worm. Hydatidosis is the most common parasitic lung disease globally.

Clinically, cough, haemoptysis and chest pain are the most common complaints. Cyst rupture may be reflected by an acute clinical deterioration and may cause anaphylaxis. 

Chest X-ray and CT may show calcified cysts, predominantly in the lower lobes.

The definitive treatment is surgery with excision of the cysts. Medical treatment with albendazole may be used for patients unfit for surgery but this may also precipitate cyst rupture.

Loffler’s syndrome

Loffler’s syndrome is a type of eosinophilic pneumonia whereby eosinophils migrate into the pulmonary tissue following transmission of parasitic larvae into the lung. The most common cause is the parasitic infection of Ascaris lumbricoides.

Its most distinguishing features are eosinophilia and parasites grown on sputum and stool culture, but this can be delayed.

Treatment is with antihelminthic agents such as albendazole. Steroids may help with the pulmonary hypersensitivity reactions.

Paragonimiasis

Paragonimiasis is caused by a trematode (fluke) found in East Asia, India, Central and South America and West Africa. The main risk factor is ingestion of undercooked seafood. Loffler’s syndrome is a possible complication, as are pleural effusions, haemoptysis and pneumothoraces.

Diagnosis is mainly via serology. Treatment is with praziquantel.

References

• Sarkar M, Pathania R, Jhobta A, Thakur B, Chopra R. Cystic pulmonary hydatidosis. Lung India. 2016;33(2):179
• T N, Marti H, Duhnsen S, G B. Pulmonary Schistosomiasis – Imaging Features. Journal of Radiology Case Reports [Internet]. 2010 Sep 1; 4(9):37–43 [accessed 23/08/22]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3303399/
• Chapman S. Oxford handbook of respiratory medicine. Oxford, United Kingdom: Oxford University Press; 2014