Diagnosis of infectious diseases

Question 1

acute serum

Answer 1

draw in first 14 days

Question 2

titers are usually zero at

Answer 2

less than 7 days

Question 3

draw a convalescent serum

Answer 3

3-6 weeks after the first serum, look for 4 forld greater titer increase due to IgG

Question 4

ELISA gives serum titer as

Answer 4

optical density

Question 5

Titer is

Answer 5

the highest dilution of serum still giving a positive result.

Question 6

What to do if you miss acute titer

Answer 6

draw convalescent titer when titer is high 3-6 weeks after start of infection

Question 7

a single positive antibody usually

Answer 7

doesn’t allow a definitive confiramtion of most acute infections, exceptions are the chronic infections, lyme disease, HIV, Hepatitis infections.

Question 8

for HIV and Lyme diesase

Answer 8

Do a western blot assay to check for presence of variety of antibody types. check for virus antigen or virus DNA or RNA- antigen immuno assay or PCR for nucleic acid.

Question 9

for hep b diagnosis

Answer 9

check for antibody markes for viral antigens and human antibodies against the virus, PCR for hep B virus titer

Question 10

Test for congenital infection

Answer 10

check for antibody titer for agents suspected of CMV, toxoplasma, test at birth, in 3-4 months

Question 11

test for baby is negative if

Answer 11

IgM absent, IgG titer from mother will drop at rate of 50% loss every month and will never go back up. in 3-4 months the baby titers are lo or negative.

Question 12

baby positive for infection

Answer 12

IgM will be positive and IgG titers will eventually go up.

Question 13

no hope rejection specifmens

Answer 13

misidentification, culture specimens received in fixative, dried out specimen on swab. Quantity insufficient for tests ordered.

Question 14

organisms requiring prompt culture if specified by doctor

Answer 14

haemophilus ducrey, anaeroves in regular transport tubes, Neisseria Gonorrhoeae in joint fluid,

Question 15

Continuous baceremia

Answer 15

volume dependent, collect 20-30 ml per set, 2 or 3 sets/ episode, a set contains 1 aerobic and 1 anaerobiv bottle per draw

Question 16

Intermittent bacteremia

Answer 16

2-3 sets before antibiotics,

Question 17

collect each set from

Answer 17

new venipuncture site with two sticks minimum.

Question 18

things to avoid in BC collection

Answer 18

not alcohol only- idophor or chlorhesidine for 2 minutes, don’t collect only 1 bottle per set, don’t initally collect greater than 5 blood culture sets to diagnose a single clinical episode. or only 1 blood culture. don’t collect blood cultures from femoral veins or venous catheters.

Question 19

True positives vs. contaminants

Answer 19

true psoitives have multiple sets and bottles are positive, positives arise within 3 days, organism isolated is typocal pathogen, Contamnants, only one bottle of several sets is positive, organism is normal skin flora type species. present in low numbers takes 5 days.

Question 20

when collecting cerebrospinal fluid

Answer 20

wear mask to avoid normal oral flora in tubes. do gram stain from cell count tube to protect culture.

Question 21

notify lab if you want throat culture for

Answer 21

GC, dipteheria, or pertussis.

Question 22

pneumonia samples

Answer 22

best sample is direct sample of lung tissue collected in operating room, second best is saliva free sputum colelced by bronchoscopy, this should have none to few epithelial cells. Third best is good cough sputum with few numbers of epithelial cells.

Question 23

cough sputum cultures

Answer 23

avoid saliva, has squamous epithelial cells and few white blood cells (pus cells.)

Question 24

on gram stain you want to see

Answer 24

more bacteria and puscells than epithelial cells.

Question 25

caontaminates species of bacteruria

Answer 25

has greater than 3 organisms in the speciman, ,

Question 26

gram correlation with significant bacteruria

Answer 26

presence of at least two bacterial cells per high power field has

Question 27

hospitalized patients with diarrhea usually caused by

Answer 27

C. Difficile toxin, occurs in patients hospitalized that have been in hospital greater than 3 days. patients with recent antibiotics and or chemo.

Question 28

special requests to tell the lab for stool sample.

Answer 28

E coli 0157:H7 , Vibrio, Yersinia.

Question 29

cultures routinely detected fro stools

Answer 29

almonella, shigella, campylobacter

Question 30

C dificille test is a

Answer 30

toxin assay on stool

Question 31

anaerobic bacterial cultures

Answer 31

live 1-3 hours at 20* anaerboic transport devices extend survival, avoid swabs.

Question 32

Don’t culture thse for anaerobes

Answer 32

fecal contaminated, midstream and cath urine. expectorated sputa, throat, nose oropharyngeal swabs, gastric contents, vaginal and cervical swabs, superficial material from skin: wounds ulcers, eschar, sinus tracts.