Common Infections Flashcards
What are the investigations for infective endocarditis?
- CXR: septic emboli can travel to the lung and cause areas of consolidation, abscesses or cavities
- Blood cultures: 3 sets are recommended as requirement for Modified Duke Criteria
- Trans-thoracic Echo (TTE): should be performed ASAP, considered positive for IE if a vegetation, an abscess or new dehiscence of prosthetic valve is detected - rapid + non-invasive, presence of normal valve morhpology and function on TTE substantially reduces likelihood of IE, difficult on obese patients and chest wall deformities.
What screening is done in suspected IE?
- Hep B surface antigen (HBsAg) indicates current Hep B infection - if it persists for >6 months following exposure then indicates chronic infection
- Hep C antibody: usually antibodies are detectable after 60 days but test can be positive as early as 8 weeks following exposure
- HIV antibody: initial screening
- HIV RNA (PCR): detects virus in the blood
- Hep B surface antibody: immunity against HepB, positive in immunised or previous Hep B infection
- Hep C RNA (PCR): detects HCV viraemia and will determine if a patient has active HepC. Usually only performed with active HepC
What are common bacterial pathogens causing IE?
- Streptococcus viridans (most common cause - 40-50%)
- Staphylococcus aureus (especially acute presentation, IVDUs)
- Staphylococcal epidermis (mainly prosthetic valves)
- Streptococcus bovis is associated with colorectal cancer
- Streptococcus mitis (viridans group streptococcus): following dental work
Why might there be culture negative endocarditis?
About 5-7% of patients with endocarditis will have sterile blood cultures. This may be due to start of abx prior to blood cultures. It may also be due to fastidious or slow growing organisms (HACEK* and Brucella); organisms unculturable with standard methods (Bartonella, coxiella burnetti) or due to non-bacterial thrombotic endocarditis (NBTE) which can be caused by SLE (causing Libman-Sacks endocarditis) or cancer.
What is HACEK?
Haemophilius aphrophilus (subsequently named Aggregatibacter aphrophilus and Aggregatibacter paraphrophilus); Actinobacillus actinomycetemcomitans; Cardiobacterium hominis; Eikenella corrdens and Kingella kingae
What investigations should be done for meningitis?
- LP
- Viral and bacterial throat swabs: helpful because a positive result suggests evidence of colonisation. Colonised organism (s) might cause meningitis - culture for bacterial analyses, PCR for viral detection
- Meningococcal PCR: on CSF or blood, valuable for diagnosing meningococcal infection particularly if patient has already had abx, haemophilus influenzae PCR and pneumococcal PCR or urine antigen test should also be consideredd
- Blood cultures: positive will provide bacterial identification and antimicrobial sensitivity to guide choice of abx
- Pneumococcal urinary antigen: sensitive, specific and rapid and can be useful for the diagnosis of pneumococcal meningitis as well as resp infections.
What tests can be done on CSF?
- Microscopy and gram stain - allow counting of RBCs and WBCs aiding differentiation between bacterial, TB or viral meningitis; gram stain; results available within few hours
- Viral PCR including HSV, enterovirus, parechovirus: useful if viral meningitis suspected, PCR used to detect a given sequence of DNA/RNA
- Culture and sensitivity: encourage growth of bacteria to guide abx choice
What is Systemic Inflammatory Response Syndrome (SIRS)?
An inflammatory state affecting the whole body, frequently a response of the immune system to infection, but not necessarily so. It is related to sepsis, a condition in which individuals meet criteria for SIRS and have known infection.
What is the criteria for SIRS?
- Body temperate <36 or >38
- HR >90 bpm
- RR > 20 breaths or arterial partial pressure of CO2 > 4.3. kPa (32 mmHg)
- WCC 12.0x10^9 cells/l or presence of >10% immature neutrophils (band forms). Band forms >3% are called a ‘left shift’
SIRS can be diagnosed when >/= 2 of these are present
What is the best treatment for septic arthritis?
Best abx for empirical treatment of septic arthritis is IV flucloxacillin. Septic arthritis is most commonly caused by gram positive cocci, especially staph aureus. As the infection is in a deep site, IV flucloxacillin is 1st line.
What is the CURB-65 score?
- Confusion
- Urea >7 mmol/l
- RR >/=30
- BP: systolic <90mmHg +/or diastolic less than/equal 60mmHg
- Aged >/= 65yrs
What are the investigations for pneumonia?
- Mycoplasma serology: mycoplasma pneumoniae is an intracellular organism which causes CAP and is not readily cultured with standard lab methods - diagnosis usually confirmed with detection of antibodies to the organisms or PCR of resp samples e.g. sputum, repeated after 2-3 weeks so can be compared.
- Urine legionella and pneumococcal antigen: legionella pneumophilia is transmitted by aerosolized water droplets from air con, water tanks, shower heads and medical equipment such as nebulisers. Legionella grows in warm stagnant water, hospitals heat their hot water to high temperature (>70 degrees) to overcome this.
- Blood cultures: recommended for all with moderate and high severity CAP, preferably before abx therapy is commenced.
- HIV test: should be offered to anyone presenting with bacterial pneumonia. If +ve, opportunistic infections will need to be considered.
When should legionella and urine pneumococcal antigen tests be done?
- Legionella antigen test only detects L. pneumophila group 1 infection which accounts for 80%. Legionella PCR on respiratory antigens has a higher sensitivity and detects all serotypes.
- Urine pneumococcal antigen tests: used in patients with CAP, especially with severe or non-responding diesase
What investigations should be done for a spike in fever during treatment?
- Blood cultures from central line/arterial line/peripheral blood cultures
- Peripheral blood cultures: can confirm bacteraemia
- CXR: compare to previous CXR for new consolidation or pleural effusion/empyema
- Blood test for beta D glucan: used in diagnostics of invasive fungal infections (component of cell wall of most fungi - rule out test)
- Culture of endotrachel secretions: may represent colonisation or infection - interpret with caution, when patients are ventilated the presence of ETT impairs mucociliary clearance and disrupts cough reflex. This promotes accumulation of the tracheobronchial secretions and increased risk of pneumonia. Formation of biofilm on surface of ETT is a universal phenomenon and has been related to pathogenesis of VAP.
What are viral haemorrhagic fevers?
This group of viruses, including Lassa fever, Crimean-Congo haemorrhagic fever, Marburg and Ebola, pose a potential risk to healthcare workers because they can be transmitted person-to-person in body fluids. Because of the serious nature of these infections, all UK hospitals have policies for the risk assessment of travellers who present unwell within 21 days of leaving countries where these infections are found. High risk patients require strict isolation and close liaison with ID and micro specialists. These infections are very rare in the UK and specialist isolation facilities are available in Newcastle and London. A full assessment of anyone presenting with fever from a risk area should be made.
