Microbiology Nuts & Bolts Test Yourself - Sepsis 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.

Carla 45 year old lady with a history of breast cancer She last had chemotherapy a week ago She presents with a fever and shortness of breath On examination she is tachycardic and hypotensive

What is the most likely diagnosis? Urinary tract infection Community acquired pneumonia Cellulitis Sepsis A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Sepsis At this stage the most that can be said about Carla is that she is probably septic Sepsis is infection with evidence of the systemic response to that infection Sepsis is a medical emergency

Carla Carla is seen immediately by the medical team and given oxygen and fluids

What blood sciences investigations should be done? FBC, U&Es, CRP FBC, Clotting, U&Es, LFTs, CRP FBC, Clotting, U&Es, LFTs, blood gas FBC, Clotting, U&Es, CRP, blood gas A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: FBC, Clotting, U&Es, LFTs, CRP, blood gas There may be other tests required as well but these are a bare minimum to manage to diagnose sepsis and manage this patient effectively The blood sciences tests involved in diagnosing severe sepsis include: –Total white blood cell count –Platelet count –Bilirubin –Creatinine –INR or APTT –Lactate CRP is not part of the sepsis diagnostic criteria, and can be normal in rapid onset sepsis

Which of the following is NOT a common cause of sepsis? Neisseria meningitidis Staphylococcus haemolyticus Streptococcus pyogenes Klebsiella pneumoniae A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Staphylococcus haemolyticus Despite it’s serious sounding name S. haemolyticus is actually one of the Coagulase-negative Staphylococci and these very rarely cause sepsis The most common causes of sepsis include: –Neisseria meningitidis –Staphylococcus aureus –Enterobacteriaceae e.g. E. coli, Klebsiella spp., Enterobacter spp. –Pseudomonas aeruginosa –Streptococcus pyogenes Sepsis can arise from infection in almost any body site

Carla Carla was diagnosed with severe sepsis Blood cultures were taken Antibiotics were started within the first hour of her admission to hospital

Which blood culture bottle should be taken first? Aerobic Anaerobic It doesn’t matter Other blood tests should be taken first A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Aerobic Blood cultures should always be taken before other blood samples, because the other blood sample collection containers are not sterile If the needle from the venepuncture equipment is contaminated from the other blood sample containers then the contaminating bacterium can grow in the blood culture causing a false positive result, also known as a pseudobacteraemia The aerobic bottle should be taken first as this is most likely to grow a pathogen –Most human pathogens are either aerobes or facultative anaerobes, in either case the bacterium will grow in the aerobic bottle –Aerobes will not grow in the anaerobic bottle, and infections only caused by anaerobes are uncommon, and usually the blood cultures are not positive in these infections anyway

Which of the following would be appropriate empirical antibiotic(s)? IV Ceftazidime IV Teicoplanin IV Gentamicin IV Piptazobactam A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: IV Piptazobactam Of the antibiotics listed, only Piptazobactam has a sufficiently broad enough spectrum of activity to cover all of the common causes of sepsis IV Gentamicin is often added to other antibiotics to treat sepsis because it has excellent bactericidal activity against Staphylococcus aureus, Enterobacteriaceae and Pseudomonas aeruginosa Ceftazidime does not have adequate activity against Gram- positive bacteria Teicoplanin has no activity against Gram-negative bacteria Gentamicin on it’s own does not cover Neisseria meningitidis or Streptococci

Carla The blood tests reveal that Carla is neutropaenic

What is the correct decision about antibiotic therapy now? Continue IV Piptazobactam Add IV Clarithromycin Change to IV Meropenem Add IV Teicoplanin A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Continue IV Piptazobactam IV Piptazobactam covers the common causes of sepsis irrespective of whether the patient is neutropaenic or not It is not necessary to change the antibiotics in response to the current blood test results

Carla The blood cultures taken from Carla are taken down to the microbiology laboratory

How are blood cultures processed in the microbiology laboratory? Urgent Gram film then culture Plated to agar for culture Loaded on to automated incubator Left at room temperature to enhance growth A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: loaded on to automated incubator The number of bacteria in a blood culture from a patient who is septic is actually very low, about 1 colony forming unit (or bacterium) per ml of blood It is therefore necessary to grow these bacteria up to sufficient numbers to be able to identify the bacterium and perform antibiotic sensitivities The blood cultures are loaded on to an automated incubator as soon as possible so that the cooler temperature of a normal room doesn’t kill the bacteria The automated incubator scans the bottles every 10 minutes in order to detect the production of carbon dioxide from living bacteria Once the incubator indicates the blood culture is positive the bottles are taken off the machine and further work begins

Carla Two days after admission no longer septic White blood cell count improving, no longer neutropaenic Remains febrile Worsening shortness of breath

Chest X ray

What is the likely diagnosis? Pneumococcal pneumonia PCP Viral pneumonitis Invasive fungal infection A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Invasive fugal infection The most likely diagnosis based upon the chest x-ray appearances and the lack of response to Piptazobactam is an invasive fungal infection Streptococcus pneumoniae would be expected to respond to Piptazobactam PCP and viral pneumonitis would have a more “ground glass” appearance Carla would no longer appear septic because her white cells are recovering from the chemotherapy and are starting to fight the infection

Carla A subsequent CT chest also shows a likely invasive fungal infection The most likely fungus is Aspergillus spp.

Which test would be most useful on a bronchoalveolar lavage (BAL) sample? Beta-D-glucan Laboratory culture Galactomannan Grocott silver stain A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Galactomannan All of the tests are of potential value in the diagnosis of invasive fungal infections but Galactomannan is the most useful for invasive aspergillosis Galactomannan is an antigen from the Aspergillus spp. cell wall which can be detected in both BAL and blood samples Detection of galactomannan in a BAL sample has a positive predictive value of 89%, a negative predictive value of 95% The PPV and NPV for the other tests is much lower Molecular tests (PCR) either alone or in combination with galactomannan are the best tests but they are expensive and not widely available

Carla A galactomannan on a BAL sample confirms invasive pulmonary aspergillosis Carla is started on antifungal treatment

Which of the following is NOT active against Aspergillus spp.? Amphotericin B Fluconazole Caspofungin Voriconazole A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Fluconazole Fluconazole has no useful activity against moulds such as Aspergillus spp. and should be regarded as treatment of Candida spp. All of the other drugs have activity against Aspergillus spp. although Voriconazole is regarded as the most active Voriconazole has a lot of side effects and drug interactions and so it is not always possible to use it to treat patients Amphotericin B and Caspofungin are IV whereas Voriconazole is available both IV and PO

Carla Carla received 6 weeks of treatment for her pulmonary aspergillosis and made a full recovery The End

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