Investigation of specific infections

Question 1

Meningitis Investigation

Answer 1

Lumbar Puncture (LP) to collect Cerebrospinal fluid (CSF)

• Blood cultures (2 sets)
• Blood for bacterial PCR (S. pneumoniae and N. meningitidis)
• FBC, Clotting, U & E’s, LFT’s, Glucose, CRP

Question 2

Encephalitis Investigation

Answer 2

• CSF requesting viral PCR specifically

Question 3

Brain Abscess Investigation

Answer 3

• Local Sampling:

Pus: surgical biopsy/drainage = Gram, culture, sensitivity (PCR)

Question 4

Ear – Acute Otitis Media Investigation

Answer 4

• Send pus if ear drum perforated

Question 5

Ear – Acute Otitis Externa Investigation

Answer 5

• Ear swab: determine cause and sensitivity

Question 6

Nose – Rhino-sinusitis (sinusitis) Investigation

Answer 6

Sample pus from operative sinus lavage (washing out sinus)

- FBC, Blood cultures in severe cases only

Question 7

Throat – sore throat (pharyngitis) Investigation

Answer 7

- Send throat swabs only if evidence bacterial infection
Additional tests:
- EBV serology
- Swab for Diphtheria
- Pus if Quinsy abscess

Question 8

Influenza Investigation

Answer 8

• Nose/ throat swabs – immunofluorescence

- PCR (sensitivity >90%, specificity 99%)

Question 9

Pneumonia Investigation

Answer 9

• Severity assessment: CURB65 score

- Score of 2-5 (mod-sever) – sputum, blood cultures, atypical screen

Question 10

Pulmonary TB Investigation

Answer 10

• Exposure testing – Mantoux, Interferon Gamma Releasing Assay
• If pulmonary symptoms – 3 sputum samples, microscopy/culture – 8 weeks, PCR

Question 11

Localised skin infections Investigations

Answer 11

• Impetigo, erysipelas, cellulitis
• Wound swabs
• Needle aspirates from cellulitis
• Blood cultures – only positive in most severe 5%

Question 12

Necrotising Fasciitis

Investigation

Answer 12

• Debride (remove) tissue - microscopy, cultures and sensitivity
• Blood cultures – 2 sets
• Bloods; FBC, U&Es, LFTs

Question 13

Diabetic foot infection Investigation

Answer 13

• Mild infection – wound swabs

- Moderate-severe infection – debride (remove) white macerated wound and collect clean bone/tissue sample

Question 14

Lower UTI – cystitis, upper UTI – pyelonephritis Investigation

Answer 14

• If dysuria and frequency, then 90% UTI
• Urine sample – WBC, RBC, epithelial cells, bacterial growth, sensitivities
• Kass criteria – threshold for “significant bacteriuria”

Question 15

UTI – Prostatitis Investigation

Answer 15

Urine mainstay of investigation – post prostatic massage

Question 16

UTI – Epididymo-orchitis Investigation

Answer 16

• Urine – cultures
• Urine – chlamydia and gonorrhoea NAAT
• If severe – bloods, blood cultures, USS +/- drainage

Question 17

Infectious diarrhoea Investigation

Answer 17

• Stool sample taken (for parasites – need 3 stool samples)
• Bloods, blood cultures
• Abdo imaging

Question 18

Helicobacter Pylori Investigation

Answer 18

• Antibody test - insensitive
• Stool antigen
• Urea breath test - gold standard for test of cure
• Biopsy urease test
• STOP PPIs (Proton pump inhibitors – antiacids; reduce stomach acid) BEFORE TESTING

Question 19

Liver abscesses Investigation

Answer 19

• Pus sample
• Stool for OCP
• Blood cultures
• FBC, U&Es, LFTs, CRP
• Hydatid serology
• Imaging – USS, CT

Question 20

Cholangitis/ cholecystitis Investigation

Answer 20

• Bloods – FBC, U&Es, LFTs, clotting, amylase
• Blood cultures
• Imaging – USS or CT
• Bile fluid or pus

Question 21

Complicated Diverticulitis Investigation

Answer 21

• Pus from abscess
• Blood cultures
• FBC, U&Es, LFTs, clotting, amylase
• CT

Question 22

Endocarditis Investigation

Answer 22

• THREE SETS OF BLOOD CULTURES – AT DIFFERENT TIMES during first 24hrs of suspected EC
• Bloods, cultures, microscopy
• Trans-thoracic Echo (TTE)
• Trans-Oesophageal Echo (TOE)

Question 23

Vascular graft infections Investigation

Answer 23

• Three sets of blood cultures at different times
• CT, PET – scan fluids around graft/fistulae
• Tissue/ fluid from around graft for culture or PCR

Question 24

Viral Hepatitis A, B, C Investigation

Answer 24

• Serology – antigen AND antibody detection
• PCR - presence of DNA/RNA = active infection
• Hep A – IgM (short term) and IgG (longer term) tested
• Hep B - acute infectious period followed by chronic period
• Hep C – only use IgG testing

Question 25

Syphilis Investigation

Answer 25

• Detection by PCR (superseded dark ground microscopy)

- Serology: IgM in primary infection, treponemal specific antibody