ABSTRACT
Our objective was to determine whether urine collection by suprapubic bladder aspiration
(SBA) improves the specificity of the group B streptococcal (GBS) latex agglutination
(LA) test by avoiding contamination of urine with GBS from perineal and rectal colonization
that can result in a positive LA test in an uninfected infant when the urine is collected
by bag. Part 1 consists of a retrospective review of the medical records of 113 infants
who had urine collected by SBA for GBS LA testing as part of evaluation for possible
sepsis. The sensitivity and specificity of the urine LA test was assessed by comparing
it with blood culture results. In part 2, a prospective analysis was performed of
19 newborns who had rectal and vaginal/penile cultures as well as urine by SBA and
bag for GBS cultures and LA. Results of LA testing on urine collected by both of these
methods were compared with results of urine, perineal, and rectal cultures. In the
retrospective review of GBS LA testing performed on 113 consecutive urine specimens
collected by SBA from neonates being evaluated for suspected sepsis, the sensitivity
and specificity were 67% and 89%, respectively, when compared with blood culture results.
Twelve infants who had a positive LA test result but a sterile blood culture (BC-,
LA+) were compared with 95 infants with both blood cultures and urine LA tests negative
for GBS (BC-, LA-). BC-, LA+ infants were more likely than those with BC-, LA- to
have an immature to total neutrophil (I/T) ratio ≥0.16 at 12 and 24 hours (p=0.04
and 0.02, respectively). In the prospective study, we found that a positive GBS LA
test can be due to perineal contamination and possibly to gastrointestinal absorption
of GBS antigen. No false positive LA test results occurred on urine obtained by SBA;
however, use of this method failed to detect the one infant with GBS bacteremia. Because
of suboptimal sensitivity and specificity, use of the GBS LA test on urine obtained
either by SBA or bag cannot be recommended for diagnosis of early onset GBS disease.
Keywords
Streptococcus group B - latex agglutination test
