Vol. 20, No. 50
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, December 11, 2001

A. Provided by Karen Fujii, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

5 outbreaks were reported to DHMH during MMWR Week 49 (December 2 - December 8):
1 outbreak of foodborne gastroenteritis associated with a restaurant (Harford Co.)
1 outbreak of gastroenteritis at a nursing home (Baltimore Co.)
1 outbreak of gastroenteritis at a nursing home (Baltimore Co.)
1 outbreak of foodborne gastroenteritis associated with an office party (Harford Co.)
1 outbreak of scabies at a nursing home (Prince George's Co.)

B. The Johns Hopkins Hospital, Department of Pathology. Information provided by Rob Law, M.D.

Effective December 5, the Cobas Amplicor® NG/CT test will be offered by the microbiology laboratory. This test will replace the Gen-Probe Pace system for detection of Neisseria gonorrhoeae and Chlamydia trachomatis. The test is a multiplex assay that permits simultaneous PCR amplification of C. trachomatis and N. gonorrhoeae target DNA as well as internal control DNA. The assay detection system utilizes an avidin-horseradish peroxidase conjugate that reacts with hybridized biotinylated amplicons and immobilized gene-specific probes within a 96-well plate.

Chlamydia are gram-negative, non-motile bacteria that exist as obligate intracellular parasites of eukaryotic cells due to their inability to synthesize ATP. C. trachomatis infections are now recognized as the leading cause of STDs in the U.S., where more that 4 million cases occur per year.

Neisseria gonorrhoeae are recognized as intracellular gram-negative diplococci. One of the most frequently reported bacterial infections in the world, it is estimated that 600,000 new cases of gonorrhea occur in the U.S.

Amplicor CT/NG testing may be performed on the following specimens:

1. Males: Urine (urethral swabs can still be used if desired)

2. Females: Cervical Swabs

(*at this time, female urine is currently being evaluated as an acceptable specimen)

Urines MUST be the initial 10-50 cc of the stream, and the patient must NOT have voided for 2 hours prior to sampling (this affects the number of free floating cells within the specimen). Swabs should be transported in the provided transport medium.

1. False negative results may occur due to polymerase inhibition. (Cervical mucous, Replens® lubricant)

2. The AMPLICOR® test is not recommended for evaluation of suspected abuse or other medico-legal indications.

3. Prevalence of infection in a population may affect performance (see below).
 
 

Prevalence (%)	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)
1	96.4	97.9	31.7	99.9
5	96.4	97.9	70.8	99.8
10	96.4	97.9	83.7	99.6
20	96.4	97.9	92.0	99.1

Prevalence (%)	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)
1	93.4	96.7	22.5	99.9
5	93.4	96.7	60.2	99.6
10	93.4	96.7	76.1	99.2
20	93.4	96.7	87.8	98.3

 

                                              AMPLICOR® CT/NG PCR³            DNA PROBE

Chlamydia (CT) Test
                Sensitivity                                   100%                                     77%

                Specificity                                    100%                                    100%

Gonorrhea (NG) Test

References:

1. Centers for Disease Control and Prevention. 1998 Guidelines for treatment of STDs, 1998. MMWR 1998:47

2. Roche Amplicor® Package insert. Roche Molecular Systems. 2000.

3. D. Fuller et al, 2000 Abstract ASM C-376. Comparison of BD PRobeTEC, Roche AMPLICOR, and Gen-PRobe PACE 2 Assays for the Detection of C. trachomatis and N. gonorrhoeae in female urine and swab specimens.