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Infection

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Topics Covered

Introduction

Respiratory infection is one of the most common reasons to be referred to a respiratory department.

Understanding why certain antibiotics are prescribed over others can be made more intuitive by looking over the principles of antibiotic prescribing. This is covered on the: Common Drugs page.

Another useful resource for understanding empirical guidelines for antibiotic prescribing is the: Tayside Antibiotic Man.

Upper Respiratory Tract Infection (URTI)

These are infections of the airway above and including the larynx:

The majority of infections are viral and self limiting within a week. A high index of suspicion of a bacterial infection is needed before any antibiotics can be prescribed.

Pharyngitis (Strep throat) and Tonsillitis

  • Viruses– SARS-CoV-2, Rhinovirus, Influenza, Adenovirus
  • Bacteria– Group A streptococcus (aka Strep pyogenes)
  • Use the FeverPAIN Criteria to determine if bacterial or viral:
    • Score of 4 = high likelihood of bacterial infection
    • Score out of 5 – each symptom gives a point:
      • Fever
      • Purulent Tonsils (pus)
      • Attend Rapidly (onset less than 3 days and have seen GP)
      • Inflamed Tonsils
      • No cough

(if bacterial also more likely to have cervical lymphadenopathy- lymph node swelling around the neck)

Infectious mononucleosis (mono/glandular fever)

Caused by Epstein-Barr Virus (EBV)

More severe symptoms associated than a simple URTI- cervical lymphadenopathy, inflamed tonsils, hepatosplenomegaly.

University students most likely cases.

If found on swab (mono spot test)- STOP all antibiotics if commenced previously.

Lower Respiratory Tract Infection

Common Symptoms

  • Upper Resp infection first – develops in to lower
  • Sputum – GREEN in bacterial infection
  • Fever
  • Cough
  • Malaise (general feeling of unwell)
  • SOB
  • Loss of appetite
  • Rigors (shivering)
  • Chest pain
  • Weight loss

Lower respiratory infections includes:

  • Acute Bronchitis – usually viral – no antibiotics
  • Acute-on-Chronic Bronchitis – exacerbation of COPD – covered on: Obstructive diseases page
  • Pneumonia

There are different types of pneumonia which tend to have different bacteria associated with them depending on where the infection came from and the baseline state of the patient:

Community Acquired Pneumonia (CAP)

Pneumonia where the infection is acquired outwith any recent medical treatment.

  • Can be Typical organisms:
    • Gm +ve
      • Streptococus Pneumoniae (most common cause in OLD -over middle age) –most common cause of pneumonia overall
      • Group A Streptococci (THE SAME AS S.PYOGENES)
      • [Staphylococcus Aureus -typically presents after a recent influenza infection- (strep. pneumoniae still more common in this scenario)] -rare as a CAP
    • Gm -ve
      • Klebsiella pneumoniae
      • Haemophilus Influenzae
      • [Pseudomonas aeruginosa] -rare as a CAP
  • Can also be Atypical (rare) organisms:
    • Legionella– Contact with water systems – i.e. changing a water tank etc (causes Legionnaires’ Disease- Legionella pneumonia)
    • Coxiella Burnetii (Q-fever) – Farm animal contact
    • Mycoplasma Pneumoniae – Young adult/child pneumonia
  • Neonates can also be infected with a currently infected mother with Chlamydia Trachomatis if delivered vaginally.
    • 50% of mothers infected with chlamydia can infect their new born. -This will progress to this pneumonia or an eye infection.

Hospital Acquired Pneumonia (HAP)

Especially in hospital, in addition to the normal CAP organisms, there are other more specific organisms that are prevalent in the hospital environment. These are typically harder to treat as they tend to be more resistant to antibiotics.

Ventilator Associated Pneumonia (VAP) particularly increases the risk of a HAP.

Organisms Associated:

  • Gm +ve:
    • MRSA – Methicillin Resistant Staph. Aureus
  • Gm -ve:
    • Pseudomonas aeruginosa

Aspiration Pneumonia

Pneumonia as a result of breathing in:

  • foreign object
  • vomiting and breathing in gastric contents

Different associated bacteria as a result: -Anaerobes and Enterobacteriaceae

Most commonly causes a lobar pneumonia on RIGHT LOWER LOBE- due to the bronchi placement being most inferior to all others.

Immunocompromised Pneumonia

Pneumonia in the immunocompromised is most challenging to treat.

Pneumocystis jiroveci, Aspergillus sp. endemic mycoses. – All fungal infections, spores are commonly found, however do not affect those with a normal immune system.

Common Investigations

  • CURB-65 score – rates the severity of possible pneumonia:
    • Confusion
    • Urea (in blood) >7 mmol/l
    • Respiratory rate ≥30
    • Blood Pressure= Any value < 90/60
    • Age 65 or over?
  • Sputum culture if score ≥ 3 – otherwise no need
    • Determines infectious organism – for more tailored antibiotic prescribing
  • Oximeter
  • Blood test – In particular CRP (if have doubt)
  • CXR – not routine – can rule out pneumonia if symptoms align with other pathology

Management

See: Common Drugs for antibiotic prescribing principles

If Pneumonia is suspected- prescribe empirical antibiotics (these are antibiotics that the bacteria that have caused the infection are most likely sensitive to- the bacteria vary by region and by type of infection – see local guidelines)

If moderate-severe and sputum sample comes back – tailor antibiotics to specific infective organism.

Other management is supportive – ie Oxygen is hypoxic, Analgesia if in pain

Tuberculosis (TB)

  • What:
    • Caused by the bacterium: Mycobacterium Tuberculosis – gram positive bacillus
    • Two types: Latent (no disease) and Active (diseased)
      • Only 5% of those infected with TB are diseased. – This is latent TB –
        • This occurs as a result of the immune system creating a granuloma around the infection to stop its spread. (A type 4 hypersensitivity reaction -CELL MEDIATED)- In this way there is no disease and the host is not infectious to others.
        • Some cases of latent TB reactivate as the TB breaks free of this granuloma to cause disease.
          • It is unclear why this happens – however a weakening of the immune system may play a part
  • Who:
    • Not common in the UK, however present in many countries throughout: Eastern Europe, Asia, Africa and South America.
    • Travelers/Immigrants from the above countries
  • Investigations
    • Mantoux Spot test – shows people as positive if vaccinated, does not pick up everyone
    • Interferon GRA (IGRA) test more sensitive
    • “Acid Fast Bacillus (AFB)” – Specific culture for TB – if positive – TB positive
    • X-ray can show classic signs of disease:
      • GRANULOMA in latent TB
      • Milliary Nodules – in severe, diffuse ACTIVE TB
  • Symptoms:
    • TB can spread throughout the body via lymphatics
    • Cough (especially if lasting for 3 weeks or longer) with or without sputum production.
    • Hemoptysis (coughing up blood)
    • Chest pain
    • Loss of appetite
    • Unexplained weight loss
    • Night sweats
    • Fever
  • Management:
    • Active TB: – 6 months total
      • THINK RIPE for 2 months:
        • Rifampicin + Isoniazid + Pyrazinamide + Ethambutol
      • THEN RI for 4 months after:
        • Rifampicin + Ioniazid
    • Latent TB- Half the drugs, Half the time:
      • JUST RI for 3 months total:
        • Rifampicin + Ioniazid

Chronic Infection

Both CF and Bronchiectasis cause damage to the mucocilliary escalator. This allows for bacteria to colonise the respiratory tract.

These bacteria do not necessarily cause disease (think of your gut microbiome) but have the potential to.

This must be taken account of on a sputum culture where:

  • Pseudomonas Aeruginosa
  • Haemophilus influenzae
    • Are both big colonisers – also a large source of infection
    • Colonisation by bacteria can still cause inflammation which can worsen bronchiectasis.
    • Exacerbations where these bacteria can cause active disease is also possible

Bronchiectasis

What:

  • Dilation of the bronchial tree due to scarring – many causes: such as repeated infections (like from CF) or obstruction – tumour
  • Permanent – scar tissue cannot be replaced and bronchioles remain dilated
    • This dilation means that mucous clearance is reduced leading to even more recurrent infections
  • Similar to Respiratory Cystic Fibrosis – just different cause

Who:

  • Anyone at risk of infection

Symptoms:

  • Repeated infections
  • Infections hard to clear- lack of response from antibiotics
  • Purulent Sputum
  • Long, persistent cough

Investigation:

  • CT scan – to visualise bronchioles -gold standard for diagnosis

Management:

  • Life long antibiotic prophylaxis (if more than 3 infections a year) – Azithromycin first line
  • Immunisation (flu)
  • Airway clearance techniques

Cystic Fibrosis

See: Paediatric Diseases Page