Microbiology Nuts & Bolts Test Yourself Session 1 Begin here

The patient in this test yourself case is entirely fictitious, however it is based on many clinical scenarios the author has come in to contact with during his medical career. Any similarity to a real case is entirely coincidental.

Steven 67 year old smoker Presents with fever & cough 1 week On examination –Temperature 38.5 o C –Decreased air-entry at the right base No recent travel abroad No pets Works as a salesman

What will be the most help in exploring the immediate differential diagnosis in this patient? FBC, CRP, Sputum culture, Chest X-ray FBC, CRP, U&Es, Sputum microscopy, Chest X-ray FBC, CRP, U&Es, Urine dipstick, Chest X-ray FBC, CRP, U&Es, LFTs, Urine MC&S, Chest X-ray A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: FBC, CRP, U&Es, Urine dipstick, Chest X-ray FBC –Total white cell count and differential gives information about the likelihood of infection and the possible aetiological agents e.g. ↑ WBC with a neutrophilia indicates likely bacterial cause –Platelets are an acute phase reactant, going up in infection and inflammation U&Es –Knowledge of renal function is essential to prescribe safely –Urea can be used to help assess severity of CAP CRP –Rises in bacterial infection Urine dipstick –Absence of leucocytes and bacterial nitrites has approximately 97% negative predictive value for UTI Chest X-ray –Part of the British Thoracic Society criteria for CAP in hospital

Steven Bloods –WBC 22 x 10 9 /L –CRP 313 –U&Es – Urea 9, Creat 133 Urine –Dipstick ++ leucs, ++ nitrites Chest X-ray

What is the most likely diagnosis? UTI Community Acquired Pneumonia UTI + Upper Respiratory Tract Infection UTI + Community Acquired Pneumonia A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Community Acquired Pneumonia (CAP) The White blood cells and CRP suggest an acute bacterial infection Even though the urine is consistent with a diagnosis of UTI the positive predictive value of this test is poor (approximately 60%) and so it does not diagnose a UTI The Chest X-ray shows right basal consolidation and so the diagnosis is CAP Note: dual pathology is rare and so it is unlikely for the patient to have both CAP and a UTI

Steven On the basis of the Chest X-ray appearances Steven is re-examined to look for signs of pneumonia

Which of the following is NOT usually a clinical sign Community Acquired Pneumonia? Crackles in the chest Dullness to percussion Increased vocal resonance Reduced chest expansion A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Crackles in the chest The clinical findings consistent with consolidation in the chest are: –Observation: decreased chest movement –Palpation: decreased chest expansion, decreased tactile vocal fremitus –Percussion: dullness –Auscultation: increased breath sounds with bronchial breathing Crackles are usually sign of heart failure or fibrosis rather than consolidation

Steven Further investigations ordered –Sputum culture –Blood cultures –Urine for Legionella antigen (Ag) Repeat clinical examination to look for signs of pneumonia

Which of these sputum appearances is consistent with a diagnosis of Community Acquired Pneumonia? Mucoid Purulent Salivary Mucopurulent A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Purulent The appearance of sputum can help in distinguishing infection from upper respiratory tract contamination when looking at sputum culture results: –Salivary Spit not phlegm, risk of contamination –Mucoid Upper respiratory tract specimen, no evidence of inflammation, therefore culture result likely to represent contamination not infection –Purulent Indicates inflammation and therefore is consistent with a deep sample from an infect chest

Steven Observations deteriorate –SaO2 92% on air –Temperature 39.5 o C –H.R. 110bpm, B.P. 115/60 –Respiratory rate 32/min –Starts having rigors

What antibiotics should the patient be started on? IV Piptazobactam + Gentamicin IV Piptazobactam + Clindamycin IV Co-amoxiclav + Clarithromycin IV Teicoplanin + Levofloxacin A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: IV Co-amoxiclav + Clarithromycin Most hospitals use a combination of a beta-lactam and a macrolide antibiotic for severe CAP Piptazobactam is unnecessarily broad spectrum for CAP Gentamicin does not penetrate into the chest very well and has no action against non-culturable bacteria” Whilst Clindamycin is often considered with the macrolides it is actually a lincosamide and has a different spectrum of activity. It has no action against non-culturable bacteria Teicoplanin + Levofloxacin are often used for severe CAP in patients who are allergic to beta-lactams however this patient has no evidence of this and therefore he would be exposed to nephrotoxic and high risk CDAD antibiotics unnecessarily

Steven Diagnosed with Community Acquired Pneumonia Starts IV Co-amoxiclav and Clarithromycin as CURB-65 score =4 –ConfusionX –Urea >7mmol/L –Respiratory Rate >30/min –BP >90systolic or <60 diastolic –Age >65 years

Which of the following is NOT usually a cause of Community Acquired Pneumonia? Legionella pneumophila Streptococcus pneumoniae Pseudomonas aeruginosa Staphylococcus aureus A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Pseudomonas aeruginosa The common causes of CAP are: –Staphylococcus aureus –Streptococcus pneumoniae –Haemophilus influenzae –Mycoplasma pneumonia –Legionella pneumophila (especially if travelled) –Chlamydia pneumoniae –Viral e.g. Influenza, Parainfluenza, Respiratory Syncytial Virus, Adenovirus Pseudomonas aeruginosa is more common if the patient has a pre-existing lung condition such as Chronic Obstructive Pulmonary Disease (COPD)

Steven Next day Bloods –WBC 27 x 10 9 /L –CRP 375 –U&Es – Urea 10, Creat 125 Urine –Microscopy >100 WBC, no epithelial cells –Culture = No growth Blood Culture –Gram-positive coccus

How would you manage the patient now? Change IV Co-amoxiclav to IV Piptazobactam Change the IV Clarithromycin to IV Levofloxacin Stop current antibiotics and start IV Meropenem Persist with Co-amoxiclav and Clarithromycin A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Persist with Co-amoxiclav and Clarithromycin There is no reason to suspect that this patient has anything other than one of the normal causes of CAP It is most likely that he needs more time to respond to the prescribed treatment or that he might need more respiratory support e.g. oxygen or non-invasive ventilation In particular, dropping the macrolide antibiotic would be a mistake as this means that unculturable bacteria are no longer covered

Steven Steven continued on Co-amoxiclav and Clarithromycin Next day he felt a little better Temperature was settling Bloods –WBC 19 x 10 9 /L –CRP 198 –U&Es – Urea 12, Creat 150 Blood Culture –Coagulase negative staphylococcus

Steven Results were followed up at 48 hours Urine – No growth Blood cultures – Coagulase negative Staphylococcus Sputum – Streptococcus pneumoniae Urine – Positive for Legionella Ag

What is the most likely diagnosis? Legionella pneumophila pneumonia Streptococcus pneumoniae pneumonia Aspiration pneumonia Staphylococcal endocarditis A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Legionella pneumophila pneumonia The urinary antigen test for Legionella pneumophila is very good –Sensitivity 95% –Specificity 95% –The main drawbacks are It only detects Serogroup 1 (there are 14 in total) however in reality almost all infections are Serogroup 1 It can cross react with Campylobacter sp. infection Growth of Streptococcus pneumoniae in the sputum can occur in the absence of pneumonia as this organism is part of the normal respiratory flora in healthy individuals as well as those with CAP The presence of a Coagulase negative Staphylococcus is the result of contamination of the blood culture at the time it was taken, usually due to poor aseptic technique

Steven Steven was diagnosed as having Legionella pneumophila pneumonia The case was notified to the health Protection Unit who under took further investigations for the source of infection.

What is the treatment of Legionella pneumophila pneumonia? IV Meropenem for 3 weeks Oral Co-amoxiclav for 3 weeks Oral Clarithromycin for 3 weeks Oral Levofloxacin for 3 weeks A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Oral Levofloxacin for 3 weeks Levofloxacin is superior to Clarithromycin for the treatment of Legionella pneumophila reducing the mortality rate from approximately 10% to 0.5% Levofloxacin has very good oral bioavailability and so if the patient is showing signs of improvement it is rarely necessary to give it by the IV route

Steven Steven was converted to oral Levofloxacin and continued for a 3 week course of treatment. He made a full recovery The source of his Legionella pneumophila was never discovered The End

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