Lecture 30 Dx Infectious Disease

Question 1

Parasite detection & dx

Answer 1

• don’t take 3 specimens in one day
• EIA tests give speed
• direct microscopic exams give completeness bc it finds parasites not part of EIA test.

Question 2

Stools or O & P

Answer 2

• Direct wet smear:
  
  • done on fresh stool mixed iodine stain
  • easy to do, but may lack sensitivity
• Preserved stools for concentrated smears
• Fecal immunoassays (fresh, frozen, preserved)
  
  • EIA: specimens used directly
  • FA: stools concentrated by centrifugation

Question 3

Physician should order complete O&P exam if Pt falls into one of these categories

Answer 3

• AIDS or other immunodef. Pt
• resident or recent immigrant from developing country
• travel to developing country or remote area
• persistent undiagnosed diarrhea

Question 4

ImmunoDx of acute infections

Answer 4

• draw an acute serum w/in 1st week or as soon as possible before 14 d; titres usually low < 7 d
• draw a convalescent serum 3-6 wk after the 1st serum
  
  • look for 4x or greater titre increase due to IgG
• If test is ELISA, titre reported as OD

Question 5

Blood cultures (BC)

Answer 5

• continuous bacteriemia
  
  • vol. dependent -> collect 20 - 30 ml per set
  • 2 or 3 sets/episode; a set contains 1 aerobic and 1 anerobic bottle per draw
• intermittent bacteremia:
  
  • 2 to 3 sets before antibiotics
• collect one aerobic and one anaerobic bottle

Question 6

CSF sample

Answer 6

• Do Gram stain from cell count tube to protect culture tube
  *

Question 7

Throat/NP cutlure

Answer 7

• Group A streptococci
• notify lab if testing or GC, diptheria, or pertussis

Question 8

Detecting agent of pneumonia

Answer 8

• best: lung tissue in OR
• 2nd best: saliva-free sputum
• 3rd best: cough sputum w few numbers of epithelial cells

Question 9

Urine culture

Answer 9

• Likely to be significant 80% of time: 1e5 CFU/ml of one organism
• Urine collection: clean catch, first morning specimen
• Gram stain w significant bacteriria: on oil immersion field, usually can see only 1 or 2 organisms = 10e4

Question 10

Nosomial infections

Answer 10

Hospital Acquired Infection (HAI)

Most evident @ >= 72 h (typical incubation period)
1/3 or more of HAI is preventable

Environmental culturing

Hospital environment does not affect infection rates
Focus on hospital staff instead.

Targeted surveillance studies

Multiple targets & levels

Airborne Precautions

Droplets <= 5 microns suspended in air
Pt placed in –ve pressure room
N95 mask

Main nosocomial infections

Catheter-induced UTI
Ventilator-Associated Pneumonia (VAP)

C diff in intestinal disease: Vancomycin-resistant organsisms (VRO) -> Rx w metronidazole, clean rooms w chlorox
Staph aureus MRSA: ARO precautions, in neonates: cord treated w antibiotics successful,
E. faecium:

Question 11

Paired acute and convalescent serum sample is necessary to:

Answer 11

• detect a 4 fold increase in total Ab titre