MICRO: Respiratory tract infections Flashcards
Covered here:
- Pneumonia
- Bronchitis
- Empyema
- Aspergillosis/PCP
- Antibiotic management of CAP/HAP
List the types respiratory defence compromise and their effects.
- 18yo female; fever, cough and malaise
- Diagnosed with flu by GP (no ABx given)
- Attended A&E with…
- T: 38C
- 87% sats on room air
- Chest clear, RR 24
- Bloods (WCC 40.8, Neut 36.3, CRP 63)
Streptococcus pneumoniae
Investigations diagnosis
- CXR - double heart border (‘Sail’ sign)
- CT - densely consolidated and collapsed lower lobe
What are the microbiological characteristics of streptococcus pneumoniae? What is it sensitive to and what is the exception?
- Alpha-haemolytic and optochin-sensitive
- Gram-positive cocci (chains and pairs)
- Optochin sensitivity shows that it may be streptococcus pneumoniae
- Almost always penicillin-sensitive
- Penicillin-resistance strains may be imported from Southern Europe (so travel history may be important)
What % of CAP is made up by S. pneumoniae?
30-50%
How does streptoccus pneumoniae RTI present?
-
Acute onset
- Severe pneumonia
- Fever and rigors
- Lobar consolidation
- Rusty coloured sputum is characteristic of S. pnuemoniae
What is pneumonia and what is the mortality/admission rate?
Pneumonia – inflammation of the lung alveoli
Patients are sick with a mortality of 5-10%
20-40% admitted to hospital
What are the clinical features of pneumonia?
- Fever
- Cough
- Abnormal CXR
- Pleuritic chest pain
- SoB
How is pneumonia classified? What are some risk factors important to consider?
Classification:
- Community-acquired
- Hospital-acquired/nosocomial (i.e. ventilator-associated)
Underlying factors to consider
- Pre-existing lung disease
- Immunocompromise
- Geography, seasons, epidemics
- Travel, exposure to animals
Why is no identification of CAP organisms usually made?
NO microbiological identification of the pathogen is made in most cases:
- Often due to difficulty obtaining a good sputum sample
- And because of early treatment with antibiotics
What are the main CAP organisms?
TYPICAL (85%)
- Streptococcus pneumoniae
- Haemophilus influenzae
ATYPICAL (15%)
- Legionella
- Mycoplasma
- Coxiella burnetii (Q fever) from exposure to farm animals (also causes hepatitis)
- Chlamydia psittaci (Psittacosis) from exposure to birds (can cause splenomegaly, rash, haemolytic anaemia)
Other organisms:
- Moraxella catarrhalis
- Staphylococcus aureus
- Klebsiella pneumoniae
What is the effect of age on CAP organisms?
- 0-1 months –> E. coli, GBS, Listeria monocytogenes
- 1-6 months –>Chlamydia trachomatis, Staphylococcus aureus, RSV
- 6 months - 5 years –> Mycoplasma pneumoniae, Influenza
- 16-30 years –> Mycoplasma pneumoniae, Streptococcus pneumoniae
What are the signs of pneumonia on examination?
- Pyrexia
- Tachycardia
- Tachypnoea
- Cyanosis
- Bronchial breathing
- Crackles
- Dullness to percussion/tactile vocal fremitus
NB: particularly in young people, you may not find symptoms localising to the chest until they decompensate.
What investigations should be done for pneumonia?
- FBC, U&E, CRP
- BCs, Sputum MC&S
- ABGs
- CXR
What are the components of the CURB-65 score?
What is bronchitis and who is usually affected?
Bronchitis – inflammation of medium-sized airways
Mainly occurs in smokers
What are the clinical features of bronchitis?
Presentation
- Cough
- Fever
- Increased sputum production
- Increased shortness of breath
- CXR is usually NORMAL
Which organisms typically cause bronchitis?
- Viruses
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
How do you treat bronchitis?
- Bronchodilation
- Physiotherapy
- Antibiotics
What does this CXR show and what organisms may be responsible?
CXR showed a cavitation:
- Staphylococcus aureus
- Klebsiella pneumoniae
- Haemophilus influenzae
- TB
Which is most likely?
All of the above
But Haemophilus influenzae is the most likely
When is H. influenzea infection more common?
In pre-existing lung disease
What % of CAP is caused by H. influenzae?
15-35% of CAP
What are the microbiological characteristics of H. influenzae?
Gram-negative cocco-bacilli (stain on chocolate agar)
Legionella pneumophilia
How is Legionella pneumophilia transmitted?
- Spread via inhalation of infected water droplets = e.g. air conditioning, hot water tanks, fountains, car wiper liquid, gyms, saunas
NB: Serious as can cause multi-organ failure
How is Legionella grown?
On a buffered charcoal yeast extract
What is a cellular feature that defines all atypical pneumonia organisms?
Pneumonia caused by organisms without a cell wall:
- Mycoplasma
- Legionella
- Chlamydia
- Coxiella
What must be considered when prescribing antibiotics for atypical pneumonias? Can you prescribe penicillins?
Cell-wall active antibiotics (e.g. penicillins) do NOT work
So need agents that work on protein synthesis like:
- Macrolides (clarithromycin/erythromycin)
- Tetracyclines (doxycycline)
What investigations are done for atypical pneumonias?
- Urinary antigen or legionella and pneumococci
- Serology for all others
Extra-pulmonary features are characteristic of CAP. True or false?
False - features such as hepatitis and hyponatraemia are characteristic in atypical pneumonias
What are the general clinical features of atypical pneumonias?
Extra-pulmonary features like hepatitis and hyponatraemia
Flu-like prodrome before fever and pneumonia
What are the features of legionella pneumophilia? How is it diagnosed? What is the treatment?
Associated with:
- Confusion
- Abdominal pain
- Diarrhoea
- Lymphopaenia
- Hyponatraemia
Investigation: urinary antigens
Sensitive to macrolides
How is Q fever transmitted? How is it diagnosed? What is the treatment?
Common in domesticated farm animals and transmitted by aerosol or milk
Investigation: serology
Sensitive to macrolides
How is chlamydia psittaci transmitted, diagnosed and treated?
Spread from birds by inhalation
Investigation: serology
Sensitive to macrolides
- 74yo woman
- SOB, fever (38.5C), right-sided pleuritic chest pain, reduced percussion note & decreased air entry right base
- PMHx IHD, CABG, AF;
- DHx warfarin
- Otherwise well
- Admitted –> commended on cefuroxime and doxycycline –> continued to spike fevers
Whta is the cause? Why did antibiotics not help?
- CXR = homogenous shadowing with meniscus level of right side (CT à empyema with collapsed lung underneath)
- Diagnosed empyema
- These are difficult to treat because they (literally bags of pus) have a wall around them and the pus itself is very acidotic which inactivates the antibiotics à hence why she continued to spike fevers even on ABx
If a RTI fails to improve on treatment what should you suspect?
Failure to improve on treatment, suspect the following:
- Empyema/abscess
- Not receiving/absorbing antibiotics
- Immunosuppression
- Resistant organisms (travel hx)
- Proximal obstruction (tumour)
- Other diagnosis (lung cancer, cryptogenic organising pneumonia
- 21yo male, from Ecuador
- Cough and WL
- U&Es normal
- Hb 10.4
- WCC 9.8
- HIV -ve
- CRP 173
- Alb 31
- What is the most likely cause?
TB
- CXR = right-sided apical shadowing, diagnosed TB
What are the microbiological features of TB?
- Staining:
- An auramine stain (left) and a Ziehl-Neelsen stain (right) will be done
- Red rods are the acid-fast bacilli
NB: if you suspect TB you must tell the lab because MC&S will test for everything but asking for TB culture and smear will lead to decontamination of the sample prior to attempting growth for TB.
What is hospital acquired pneumonia?
- A pneumonia onset >48 hours in hospital
- Patients have often had previous antibiotics and maybe even ventilation
What are the most common causes of HAP?
- Enterobacteriaciae (e.g. E. coli, K. pneumoniae) – 31%
- Staphylococcus aureus – 19%
- Pseudomonas spp – 17%
- Haemophilus influenzae – 5%
- Acinetobacter baumanii – 4%
- Fungi (Candida spp) – 7%
Which investigation is desirable to diagnose HAP?
Bronchial lavage (differentiate upper respiratory from lower respiratory flora)
- 64yo retired general
- Treated for lymph node TB
- Increasing SOB, non-productive cough, chest exam normal
- CXR = bilateral ground-glass shadowing (“bat’s wing”)
What can be seen on this CXR and name a cause?
CXR shows bilateral ground-glass shadowing (you can see the pulmonary markings through the opacification) in a “bat wing” formation (i.e. centrally)
May be caused by PCP
What type of organism is Pneumocystic jirovecii (PCP)? Where is it found normally?
Protozoan
In the environment
What are the clinical features of PCP?
- Insidious onset
- Dry cough
- Weight loss
- SOB
- Malaise
- NOTE: the walk test (attaching an oxygen saturation probe and asking the patient to walk) will show desaturation on exertion
How do you diagnose, treat and prevent PCP?
Investigations: bronchoalveolar lavage
Treatment: co-trimoxazole (septrin)
Prophylaxis: co-trimoxazole
What are the microbiological features of PCP? (Why is the term PCP technically wrong?)
Immunofluorescence assay shows the characteristic cysts which resemble crushed ping-pong balls and are present in aggregates of 2-8 (and not to be confused with Histoplasma or Cryptococcus, which typically do not form aggregates of spores or cells)
PCP may also be detected by Silver stain in cytology labs
Pneumocystic carinii penumonia - only found in rats and terminilogy no longer used.
- 22yo man, chemotherapy for leukaemia
- Prolonged neutropenia (<1.0), fevers, raised inflammatory markers
- ABx so far = meropenem, ciprofloxacin, vancomycin, tazocin, ganciclovir
- CT thorax = non-specific (interstitial) changes on the CT scan
- Aspergillus fumigatus
What is shown below?
Hyphae of aspergillus on the right
What are the 3 types of respiratory phenotypes of aspergillus fumigatus infection?
- Allergic bronchopulmonary aspergillosis (ABPA)
- Chronic wheeze
- Eosinophilia
- Bronchiectasis
- Aspergilloma
- Fungal ball, often in pre-existing cavity
- May cause haemoptysis
- Invasive aspergillosis
- Immunocompromised
- Treatment: amphotericin B
What are the clinical features of ABPA?
- Chronic wheeze
- Eosinophilia
- Bronchiectasis
What are the clinical features of aspergilloma?
- Fungal ball, often in pre-existing cavity
- May cause haemoptysis
What are the clinical features of invasive aspergillosis?
- Immunocompromised
- Treatment: amphotericin B
What RTI can be caused in the following conditions?
- HIV
- Neutropenia
- BM transplant
- Splenectomy
- HIV
- PCP, TB, Atypical mycobacteria
- Neutropoenia
- Fungi (e.g. Aspergillus spp)
- Bone Marrow Transplant
- CMV
- Splenectomy
- Encapsulated organisms (S. pneumoniae, H. influenzae, malaria)
What general invetigations are used to diagnose LRTI?
- Sputum/induced sputum -take 24-48hrs
- Blood cultures
- BAL
- Pleural fluid
- Antigen tests
- Antibody tests
- Immunofluorescence
- PCR
Which antigen tests are used in the diagnosis of LRTI?
- Limited urine antigen tests available for: Legionella pneumophila + Streptococcus pneumoniae
Send in severe CAP
Which RTI are antibody tests useful in diagnosis?
- Only useful on paired serum samples (one acutely unwell and another when getting better). Usually collected on presentation and 10-14 days later + looks for a rise in antibody level over time
Most useful organisms to send antibody tests for because they are difficult to culture:
- Chlamydia
- Legionella
What RTI can be diagnosed using immunofluorescence?
- Antibody is labelled with fluorescent dye
- Often used in virology
- PCP immunofluorescence is the most commonly used one in microbiology labs - PCP may also be detected by Silver stain in cytology labs
What is the general antibiotic management of CAP?
Antibiotic therapies of RTIs – “I would consult the local guidelines”
CAP: Empirical Therapy (each hospital has its own guidelines)
- Mild-Moderate:
- Amoxicillin [OR erythromycin/clarithromycin]
- Moderate-Severe
- Needing hospital admission: Co-amoxiclav (augmentin) AND clarithromycin
- Allergic: Cefuroxime AND clarithromycin
What is the general antibiotic management of HAP?
HAP: Empirical Therapy (need a lot of gram -ve cover)
- 1st Line - Ciprofloxacin ± vancomycin
- 2nd Line/ITU - Piptazobactam AND vancomycin
- Specific Therapy:
- MRSA: Vancomycin
- Pseudomonas: Piptazobactam OR ciprofloxacin ± gentamicin
- 21yo man, no PMHx, smoker, drinker
- Presented cough, SOB, sats 89% room air, hypotensive
- CXR = RUZ pneumonia
- What other treatment is required?
- Treatment:
-
Cefuroxime and clarithromycin (hypotensive = query allergic)
- Worried about H. influenzae and covers for atypicals
- Fluid resuscitation
- Supplemental O2
- Senior support requested
-
Cefuroxime and clarithromycin (hypotensive = query allergic)
Coamox and clarithromycin is more correct because cef and clarithromycin is not used as much
Same case:
- 4 hours later, intubated and ventilated
- Day 2 ITI blood cultures grew streptococcus pneumoniae à cleared up by 2 months after admission
How do you prevent pneumonia in the young population and adults?
- Smoking cessation
- Vaccination:
- Childhood immunisation schedule
- Adults à influenza annually, pnemovax every 5 years
What common illness is this ?
SARS-CoV-2
Bilateral interstitial changes
Focal changes may be seen on CT
