summary of the diagnostic value of specific microbiological investigations

Summary of the diagnostic value of specific microbiological investi-

gations

Test Diagnostic value

False posi-tive rate

False nega-tive rate

Blood culture ++++ - +++ Viral antigen detection (nasopharyngeal aspirate) +++ - +

Viral culture +++ - ++ Serum antigen ++ + ++ Urine antigen + ++ ++ Paired antibody titre +++ + ++ Bacterial culture of na-sopharyngeal secretions

- +++ +

Lung puncture culture ++++ - +

Blood culture• Technique

– Minimal 1~3 mL each– Different venipuncture (≥2 sets)– Central catheter + Peripheral culture

• Colonized bacteria – possibility of contami-nation

Blood culture

Blood culture

Gram stain

Interpretation of blood culture• Almost always

important– S. aureus– S. pneumoniae– S. pyogenes (GAS)– S. agalactiae (GBS)– H. influenzae– Enterobacteriaceae

(E. coli, Klebsiella, etc..)– Bacteroidaceae– P. aeruginosa– Candida species

• Possible contaminant– P. acnes– Corynebacterium species– Bacillus species– CoNS (coagulase negative

Staphylococci, S. epider-midis)

– S. viridans– Peptostreptococcus

Most causative pathogens are compatible with clinical syn-drome

Most causative pathogens will grow within 72 hours

Nasopharyngeal aspirate collection

• Nasopharyngeal aspirate – Virus culture / PCR

Early diagnosis of viral infection

Microscopy – LM– EM

Detecting antigen– IF staining– Solid phase immunoassay (ELISA, RIA, LA), – Immunochromatography

Detecting nucleic acid– nucleic acid amplification (PCR, etc.), – nucleic acid hybridization

Tzank test of HSV Vesicular Lesion

Ultrastructural Characteristics of SARS-Asso-ciated Coronavirus Grown in Vero E6 Cell

100 nm

Indirect Immunofluorescent staining

Immunofluorescent staining

• Indirect IF Staining for RSV, • Specimen: Nasal aspirate

• Indirect IF Staining for PIV3 • Specimen: Nasal aspirate• Confocal microscopy

Antigen Detec-tion

by ELISA

Direct Method

Indirect Method

Indirect ELISA for RSVSpecimen: Nasal aspi-rate

Immunochromatography

Conventional method vs. RT-PCR

Virus identified No. detected by RT-PCR(% of total episodes)

Respiratory syncytial virus 122 (23.7) 596 (14.7)Adenovirus 35 (6.8) 243 (6.0)Parainfluenza virus type1 11 (2.1) 30 (0.7)

type 2 ND 23 (0.6)

type 3 32 (6.2) 195 (4.8)

type 4 ND 2 (0.05)Influenza virus A 24 (4.7) 117 (2.9)

B 9 (1.8) 47 (1.2)

Total 316 (61.4) *

*More than 1 virus were isolated from 36 patients (11.4%) among 514 patients, Sep 2000-Aug 2005.**1,270 strains of viruses were isolated from 1,234 out of 4,058 cases (30.4% of total patients), Nov 1990-May 2002. More than 1 virus were isolated from 36 patients.

Detection by conventional method (% of total episodes)

1,270 (30.4) **

RhinovirusMetapneumovirusCoronavirus, conventionalCoronavirus NL63BocavirusUnknown

40 (7.8)26 (5.0) 1 (<1) 9 (1.8)58 (11.2)

ND ND ND ND ND 17 (0.3)

Choi EH et al. Clin Infect Dis 2006;43:585-92