INVESTIGATION OF INFECTIONS Flashcards
Meningitis/Central nervous system infections
Meningitis: Inflammation of the meninges. Caused by viruses, bacteria, mycobacteria, fungi, parasites.
Test with: Lumbar Puncture (LP), collect Cerebrospinal fluid (CSF) and 2 sets of blood cultures.
- Encephalitis: Inflammation of brain- usually viral (Herpes viruses). CSF requesting Viral PCR specifically
- Brain Abscess: Wide aetiology: bacterial, mycobacterial, fungal, parasitic. History (patient factors) can narrow down: Ear, Sinuses, Blood, post-op etc. LP should be discouraged (rarely positive, high risk)
Local Sampling: Pus: surgical biopsy/drainage = Gram, culture, sensitivity (PCR) and Blood Cultures
Pharyngitis/Otitis/ENT Infections
Ear: Acute Otitis Media: Clinical diagnosis, viral and bacterial, send pus if ear drum perforated
Otitis Externa: Ear swab: determine cause (bact., fungal etc.) and sensitivity
Nose: Sinusitis: Majority viral. Secondary bacterial infection. Caused by upper respiratory flora. Sample in all but severe cases is unhelpful Severe cases: Pus from operative sinus lavage, FBC, Blood Cultures etc.
Throat: Pharyngitis: Sore Throat (pharyngitis) Majority are viral. Send throat swabs only if evidence bacterial infection. Looking only for B-Haem Streps. Additional tests: EBV serology, Swab for Diphtheria, Pus if Quinsy abscess and Diphtheria.
Respiratory tract infections
Influenza: Seasonal, Sporadic vs. Epidemic, highly transmissible. Not necessary to test everyone.
Test: Those who may require treatment and at risk of transmitting with Nose/throat swabs.
PCR is better than Immunofluorescence as its more sensative, specific faster and cheaper.
Pneumonia: Pneumonia is a clinical diagnosis based on respiratory symptoms, signs and chest XR changes
Severity assessment CAP= C(U)RB65- score out of (4)5. CRP may help guide diagnosis and antibiotic need
Low (0-1): No investigations required (NICE CG191)
Mod-Severe (2-5): Sputum, Blood Cultures,
Atypical Screen= Urine for Legionella antigen; Nose/throat for Mycoplasma PCR. Might include Serum
Pulmonary TB: Disease which requires 1. Exposure then 2. reactivation at later stage in life.
Exposure testing: Mantoux and Interferon G Releasing Assay
(QuantiFERON-TB, T-Spot TB) Rely on intact immune system. Pulmonary symptoms: 3 sputum samples, Microscopy & Culture (for 8 weeks) and PCR- Rapid, costly, lower sensitivity
Atypical Infection (immunocompromised): Haemato-Oncology- on chemotherapy, solid organ transplant, Steroids, Diabetes, CKD, Underlying disease (HIV, Congenital, liver etc.) and Travel
Viral (eg. RSV, CMV)- viral PCR
Fungal (eg. Aspergillus)- Culture, Aspergillus Antigen. Pneumocystis- PCP PCR. Not looked for routinely, need to guide lab with history.
Skin and soft tissue infections
Localised: impetigo, erysipelas, cellulitis
Wound swabs: not helpful from intact skin. Send blister fluid or abscess pus
Needle aspirates from cellulitis: Poor- only determine pathogen in 10-30% cases
Blood cultures: only positive in most severe 5%- send if sepsis
Severe/extensive: Necrotising fasciitis
Rapidly spreading synergistic infection. Surgical Emergency, high mortality. Debrided tissue/ pus
Blood Cultures (X2). Bloods: FBC, U&E’s, LFT’s, CRP
Diabetic Foot Infection
Non-infected Wounds or Ulcers
“Smelly” “weeping” “exudate” are not evidence of infection. Do not send swabs
Mild infection : Wound swabs: Sens. 49% / Spec. 62%
Mod/Severe (Deep) Infection: Debride wound then collect “clean”. Bone or Tissue sample- specialist
Urinary tract infections
Lower UTI and Upper UTI (pyelonephritis).
Clinical Diagnosis supported by the Microbiology
If dysuria and frequency then probability of UTI >90%
Urine Sample: WBC, RBC, Epithelial Cells, Bacterial growth, Sensitivities
Interpretation: Kass Criteria: threshold for “significant bacteriuria” and Automated analysers: microscopy to predict culture positivity
Prostatitis: 50% with recurrent UTI’s and 90% of febrile UTI’s have prostatitis. Urine mainstay of investigation
Epididymo-orchitis
2 main aetiologies: Enteric/UTI or STI
Urine- sent for cultures. Urine- sent for Chlamydia and Gonorrhoea NAAT (PCR)
If Severe: Bloods, blood cultures, USS +/- drainage
Gastrointestinal infections
Infectious diarrhoea: Viral gastroenteritis, Bacterial, Parasitic infection and Clostridium difficile infection (CDI) Helicobacter pylori infection
Wide range of pathogens: Viruses (norovirus, rotavirus), Bacteria (Campylobacter, Salmonella, Shigella, E coli 0157, Vibrio), Parasites (Cryptospordium, Giardia, foreign travel) and C. difficile infection (CDI)
Majority of viral and bacterial disease is self-limiting
Stool Sample
Liver abscess
Pyogenic (bacterial), Hydatid or Amoebic
History to guide aetiology, Pus (if safe to drain), Stool for OCP, Blood Cultures, FBC, U&E’s, LFT’s, CRP, Hydatid serology
Imaging: USS/CT
Cholangitis/cholecyctitis
Bloods: FBC, U&E’s, LFT’s, Clotting, amylase.
Blood Cultures. Imaging: USS or CT. Bile fluid/ Pus (if aspirated/drained)
Diverticulitis
Uncomplicated vs. complicated
Complicated= abscess, fistula, perforation, obstruction
Pus from abscess, Blood Cultures, Bloods: FBC, U&E’s, LFT’s, Clotting, amylase and Imaging: CT
Hepatitis/Syphilis
Hepatitis A, Hepatitis C & Hepatitis B
Serology comprises ANTIGEN and ANTIBODY detection. PCR detects DNA or RNA from living or dead organisms
Usually presence of DNA/RNA suggests active infection.
Syphilis –> Early (Primary and Secondary), Latent (Tertiary- gummatous, neuro, cardiovacular) and Congenital. Detection by PCR.
Serology: Screening test including IgM in Primary infection, Treponemal Specific Antibody (eg. TPPH, TPHA)
Non-Treponemal Specific Antibody (eg. VDRL, RPR). Expressed as dilution (1:16; 1:32 etc.).
Vascular infections
Heart Valves (endocarditis): Native, Prosthetic. Vessels- Mycotic aneurysms, Prosthetic Vascular Graft Infections.
Endocarditis: Blood cultures fundamental to management (96% positivity)
3 sets of Blood Cultures should be taken at different times during first 24 hours in all patients with suspected endocarditis.
Endocardiograohy and FBC should be done.
Vascular Graft Infections: 3 sets of Blood Cultures should be taken at different times during first 24 hours in all suspect patients but lower culture positivity rate than endocarditis.
Other investigations: Imaging: CT, PET, WBC scan- fluid around graft, fistulae, Tissue/fluid from around graft-
for culture or PCR.
