JOURNAL OF CLINICAL MICROBIOLOGY, Nov. 2003, p. 5288–5290 Vol. 41, No. 11
0095-1137/03/$08.00�0 DOI: 10.1128/JCM.41.11.5288–5290.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Infections in International Pregnancy Study: Performance of the
Optical Immunoassay Test for Detection of Group B Streptococcus

Jadsada Thinkhamrop,1* Sompop Limpongsanurak,2 Mario R. Festin,3 Sean Daly,4 Anne Schuchat,5

Pisake Lumbiganon,1 Elizabeth Zell,6 Tsungai Chipato,7 Aye Aye Win,8 Mindy J. Perilla,5
Jorge E. Tolosa,9 and Cynthia G. Whitney5

Department of Obstetrics and Gynecology, Faculty of Medicine, Khon Kaen University, Khon Kaen,1 and Department of Obstetrics
and Gynecology, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Bangkok,2 Thailand; Department of Clinical

Epidemiology, University of the Philippines, Manila, The Philippines3; Coombe Women’s Hospital, Dublin, Ireland4;
Respiratory Diseases Branch5 and Biostatistics and Information Management Branch,6 Division of Bacterial and

Mycotic Diseases, National Centers for Infectious Diseases, Centers for Disease Control and Prevention,
Atlanta, Georgia; Department of Obstetrics and Gynaecology, University of Zimbabwe School

of Medicine, Harare, Zimbabwe7; Department of Obstetrics and Gynaecology, Institute
of Medicine, Yangon, Myanmar8; and Department of Obstetrics and Gynecology,

Divisions of Research in Reproductive Health and Maternal-Fetal Medicine,
Thomas Jefferson University, Philadelphia, Pennsylvania9

Received 28 February 2003/Returned for modification 16 April 2003/Accepted 27 August 2003

We evaluated the Strep B optical immunoassay (OIA; ThermoBiostar, Inc.) for detecting light and heavy
group B streptococcus colonization in 1,306 pregnant women. The women were examined at 20 to 32 weeks
gestation and were from six countries. Compared to culture, the sensitivity and specificity of OIA were 13.3 and
98.4%, respectively, for light colonization and 41.5 and 97.7%, respectively, for heavy colonization.

Heavy colonization with group B streptococcus (GBS) may
place women at high risk of delivering preterm, low-birth-
weight infants (10, 11, 15). Earlier recognition of such high-risk
women would be useful for intervention strategies. Detection
of heavy colonization has traditionally relied on culture meth-
ods, which may not be feasible in some health care settings and
require 1 to 3 days before results are available. Unfortunately,
most rapid GBS tests have poor sensitivity (7, 13). The Strep B
optical immunoassay (OIA; ThermoBiostar, Inc., Louisville,
Colo.) is a rapid method which may have higher sensitivity for
dense GBS colonization (14). We evaluated the performance
of this test in an international, multicenter study.

We conducted the study at institutions participating in the
Global Network for Perinatal and Reproductive Health (http:
//www.tju.edu/obgyn/rih/global.cfm). Centers were located in
Khon Kaen and Bangkok, Thailand; Manila, The Philippines;
Harare, Zimbabwe; Yangon, Myanmar; Dublin, Ireland; and
Philadelphia, Pennsylvania. Participants were enrolled in the
study between June 1999 and May 2001. Women attending
prenatal care clinics and at 20 to 32 weeks gestation were
eligible. Exclusion criteria included vaginitis symptoms, fever,
vaginal bleeding, multiple pregnancy, use of antibiotics in the
past 2 weeks, and active labor. Informed consent was obtained.
The study was approved by institutional review boards at all
study centers and supporting institutions.

At enrollment, study personnel conducted an interview and
collected specimens. A sample for GBS rapid testing was col-
lected from the cervix and lower vagina using a ThermoBiostar

swab. OIAs were read by study site laboratory personnel and
by the manufacturer’s laboratory personnel. OIA kits and
swabs were supplied by ThermoBiostar.

Methods for GBS culture and quantitation replicated those
used in the Vaginal Infections and Prematurity Study (16).
After collection of the OIA specimen, a Dacron swab (Copan
swab) was used to collect a specimen from the cervix and lower
vagina. Samples were streaked onto blood agar plates using the
four-quadrant method and then placed into Lim broth (Todd-
Hewitt broth containing selective antimicrobial agents). A
clean catch urine specimen was collected for GBS culture on
blood agar. Suspect colonies showing �-hemolysis were iden-
tified as GBS using latex agglutination. Heavy colonization was
defined as isolation of GBS from either urine or direct plating
on blood agar. Light colonization was defined as isolation of
GBS from Lim broth alone. Dense GBS colonization was de-
fined as growth in the third or fourth quadrant streaked on the
blood agar plate (14).

Data were entered by using Epi-Info version 6 (9) and trans-
mitted to the Centers for Disease Control and Prevention
monthly. We calculated the sensitivity, specificity, positive pre-
dictive value, and negative predictive value of the OIA using
culture results as the “gold standard.” The chi-square test was
used to compare the results of OIA readings done by the
manufacturer’s staff versus the readings done by study center
personnel.

We enrolled 1,306 women; their mean age was 26.6 years,
and the mean gestational age was 26.3 weeks. GBS coloniza-
tion was the highest in Philadelphia, Pa., (22.1%) and lowest in
Yangon, Myanmar (7.1%). The rate of GBS isolation was
higher from Lim broth culture than from other methods (Table
1).

Compared to culture, the sensitivity of OIA for detecting

* Corresponding author. Mailing address: Department of Obstetrics
and Gynecology, Faculty of Medicine, Khon Kaen University, Khon
Kaen 40002, Thailand. Phone: 66-43-246445. Fax: 66-43-348395. E-
mail: Jadsada@kku.ac.th.

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any GBS colonization was 25.7% (95% confidence interval
[CI], 19.0 to 33.6%) and ranged from 6.3% (95% CI, 0.3 to
32.3%) in Yangon, Myanmar, to 53.3% (95% CI, 27.4 to
77.7%) in Philadelphia, Pa. OIA sensitivity was 13.3% for
lightly colonized women, 41.5% for heavily colonized women,
and 68.4% for densely colonized women (Table 2). OIA sen-
sitivity and specificity were 50.0 and 97.6%, respectively, com-
pared with culture on blood agar and 26.8 and 98.4% com-
pared with Lim broth. The OIA was positive in 1.4% of women
who were negative by all culture methods. OIA test readings
performed by the manufacturer and by study site personnel
were similar (kappa of 0.701); the sensitivities from study site
personnel and manufacturer readings was 29.7% (95% CI, 22.5
to 37.9%) and 25.7% (95% CI, 19.0 to 33.6%), respectively.

Our study demonstrated that the sensitivity of OIA to detect
GBS colonization compared with that of culture was low, al-
though the sensitivity of OIA in detecting heavy or dense
colonization was higher than its sensitivity for detecting light
colonization. Our findings confirm earlier work that found
reliance on blood agar alone was insensitive for detecting light
colonization and that comparing rapid detection methods with
blood agar alone falsely elevated the sensitivity of these tests.
Enrichment broth media, such as Lim broth, enhance GBS
growth while suppressing growth of other bacteria, thus im-
proving identification in specimens with low bacterial inoculum
(3, 6).

In previous studies, the performance of the OIA has been
compared with selective broth media. The specificity was uni-
formly high, 85 to 98%, similar to the 98.4% in our study.
Conversely, previously reported test sensitivities varied widely
but were generally higher (37 to 81%) (2, 5, 7, 12–14, 17–19)

than the value we found (26.8%). The most important reason
for this variability may be the extent to which the subjects were
colonized. The sensitivity of the OIA has been higher (61 to
100%) when compared with third- and fourth-quadrant posi-
tive blood agar cultures (2, 5, 7, 12–14). Our finding was within
this range (68.4%).

Our study had limitations, as it did not evaluate the perfor-
mance of the OIA 4 to 5 weeks before delivery or at delivery,
when it would have the most clinical value (8). However, the
average gestational age for our participants was 26.3 weeks, a
time when the fetus is considered viable in many centers,
making our data potentially useful for evaluating the role of
GBS in preterm birth. We did not collect specimens from the
rectum; collecting both rectal and vaginal cultures increases
the detection of GBS carriage in pregnant women (1). If we
had collected rectal specimens, we would have identified more
GBS carriers, and the OIA performance would have been
worse.

In conclusion, the low sensitivity of the Strep B OIA may
limit its usefulness for detecting GBS in pregnant women,
although the best performance of the test is in women who are
heavily colonized and who therefore may be at highest risk for
complications due to GBS infection. New tests, such as the
newly licensed PCR test, may provide other options (4). For
now, culture of specimens from the rectum and lower vagina
remain the gold standard for detecting GBS colonization in
pregnant women (8).

This project was performed with the financial support of the Rock-
efeller Foundation; the Respiratory Diseases Branch, Division of Bac-
terial and Mycotic Diseases, National Center for Infectious Diseases;
the Prevention Committee and the Office of Minority and Women’s
Health, Centers for Disease Control and Prevention, Atlanta, Ga.;
USAID; INCLEN; and Thomas Jefferson University.

We thank the Rockefeller Foundation; the Respiratory Diseases
Branch, Division of Bacterial and Mycotic Diseases, National Center
for Infectious Diseases; the Prevention Committee and the Office of
Minority and Women’s Health, Centers for Disease Control and Pre-
vention, Atlanta, Ga.; USAID; INCLEN; and Thomas Jefferson Uni-
versity for technical support on this project. In addition, we thank
ThermoBiostar, Inc., for supplying the OIA kits and for technical
support for this study.

J. Thinkhamrop, S. Limpongsanurak, M. Festin, S. Daly, A. Schu-
chat, P. Lumbiganon, E. Zell, T. Chipato, A. A. Win, M. J. Perilla, J. E.
Tolosa, and C. G. Whitney are members of the Global Network for
Perinatal and Reproductive Health (GNPRH), Department of Obstet-
rics and Gynecology, Thomas Jefferson University, Philadelphia, Pa..
GNPRH study centers and coinvestigators follow: Khon Kaen Univer-
sity (Khon Kaen, Thailand), Unchalee Tatttawasart, Kaewjai Kham-
suk, and Ladda Sriboonreung; Chulalongkorn University (Bangkok,

TABLE 1. Prevalence of GBS according to various culture methods
and OIA by study center

Study site (no. of samples)

Prevalence (%) of GBS by method

Lim broth
culture

Blood agar
culture

Urine
culture

OIA

Dublin, Ireland (203) 11.8 3.5 3.5 3.5
Yangon, Myanmar (226) 7.1 0.4 0.0 0.4
Manila, The Philippines (200) 6.0 0.0 2.5 5.0
Bangkok, Thailand (200) 12.0 3.0 3.5 1.5
Khon Kaen, Thailand (200) 14.5 8.0 4.0 4.5
Philadelphia, Pa. (68) 19.1 16.2 14.0 14.7
Harare, Zimbabwe (209) 11.7 5.3 4.9 7.7

All study sites (1,306) 10.9 4.0 3.5 4.3

TABLE 2. Diagnostic performance of OIA for detection of vaginal carriage of GBS compared to culture in women with light, heavy, and
dense GBS colonization (n � 1,306)

GBS colonization
levela

Performance characteristicb

Sensitivity Specificity Positive predictive value Negative predictive value

Light 13.3 (7.1, 22.9) 98.4 (97.5, 99.0) 37.9 (21.3, 57.6) 94.1 (92.5, 95.3)
Heavy 41.5 (29.7, 54.4) 97.7 (96.6, 98.4) 48.2 (34.8, 61.8) 97.0 (95.8, 97.8)
Dense 68.4 (43.5, 86.4) 96.5 (95.2, 97.5) 24.5 (14.2, 38.6) 99.5 (98.8, 99.8)

a The GBS colonization levels were defined as follows: light, isolation of GBS from Lim broth alone; heavy, isolation of GBS from either urine or direct plating on
blood agar; dense, growth in the third or fourth quadrant streaked on the blood agar plate (14).

b The four performance characteristics, sensitivity, specificity, and positive and negative predictive values, are all given as percentages. The 95% CIs are given in
parentheses.

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Thailand), Sompop Limpongsanurak, Surasith Chaithonhgwattana,
Pongpun Nunthapisud, Sumanee Nin-gate, and Wanwadee Sripitak;
Coombe Women’s Hospital (Dublin, Ireland), Amanda Cotter, Julie
Grantham, and James Fagan; Institute of Medicine, Women’s Central
Hospital (Yangon, Myanmar), Kyi Kyi Thinn, Win Win Maw, Cho Cho
Oo, MarLar Win, Thuzar Han, Mya Mya Aye, Tin Ohn Myat, and
Katherine Ba-Thike; University of Zimbabwe (Harare, Zimbabwe),
Alexio Mashu, Laina Chidede, Marshall Munjoma, Travor Ny-
amurera, and Evelyn Mudzviti; University of the Philippines (Manila,
The Philippines), Guadalupe N. Villanueva, Maybelle Cagayan, Con-
cepcion Ang, Francis Sarmiento, Daniel Morales, and Celeridad Padri-
nao; Population Council (Bangkok, Thailand), Josephine Sauvarin,
Christopher Elias, and Washiraporn Suramaythangkoon; Centers for
Disease Control and Prevention, Falgunee Parekh, Carolyn Wright,
Richard Facklam, and John Elliott; Department of Obstetrics and
Gynecology, University of Alabama at Birmingham, William Andrews,
Martha Lyon, Sue Cliver, and Robert Goldenberg; Thomas Jefferson
University, Catherine Farrell, Babu Cheku, Tracey James, Letitia Lee,
Michelle Di Vito, Michelle Pollino, Donald Jungkind, Jim Bondi,
Vincenzo Berghella, Jay Goldberg, Ratana Komwilaisak, and Jennifer
Culhane.

REFERENCES

1. Badri, M. S., S. Zawaneh, A. C. Cruz, G. Mantilla, H. Baer, W. N. Spellacy,
and E. M. Ayoub. 1977. Rectal colonization with group B streptococcus:
relation to vaginal colonization of pregnant women. J. Infect. Dis. 135:308–
312.

2. Baker, C. J. 1996. Inadequacy of rapid immunoassays for intrapartum de-
tection of group B streptococcal carriers. Obstet. Gynecol. 88:51–55.

3. Baker, C. J., J. C. Clark, and F. F. Barrett. 1973. Selective broth medium for
isolation of group B streptococci. Appl. Microbiol. 26:884–885.

4. Bergeron, M. G., D. Ke, C. Ménard, F. J. François, M. Gagnon, M. Bernier,
M. Ouellette, P. H. Roy, S. Marcoux, and W. D. Fraser. 2000. Rapid detec-
tion of group B streptococci in pregnant women at delivery. N. Engl. J. Med.
343:175–179.

5. Boyer, K. M., C. A. Gadzala, P. D. Kelly, D. E. Fisher, J. B. Paton, and S. P.
Gotoff. 1983. Selective intrapartum chemoprophylaxis of neonatal group B
streptococcal early-onset disease. I. Epidemiologic rationale. J. Infect. Dis.
148:795–801.

6. Boyer, K. M., C. A. Gadzala, P. D. Kelly, L. I. Burd, and S. P. Gotoff. 1983.
Selective intrapartum chemoprophylaxis of neonatal group B streptococcal
early-onset disease. II. Predictive value of prenatal cultures. J. Infect. Dis.
148:802–808.

7. Carroll, K. C., D. Ballou, M. Varner, H. Chun, R. Traver, and J. Salyer.

1996. Rapid detection of group B streptococcal colonization of the genital
tract by a commercial optical immunoassay. Eur. J. Clin. Microbiol. Infect.
Dis. 15:206–210.

8. Centers for Disease Control and Prevention. 2002. Prevention of perinatal
group B streptococcal disease—revised guidelines from CDC. Morb. Mortal.
Wkly. Rep. 51(RR11):1–22.

9. Dean, A. G., J. A. Dean, D. Coulombier, et al. 1995. Epi-Info version 6: a
word processing, database, and statistics program for epidemiology on mi-
crocomputers. Centers for Disease Control and Prevention, Atlanta, Ga.

10. McKenzie, H., M. L. Donnet, P. W. Howie, N. B. Patel, and D. T. Benvie.
1994. Risk of preterm delivery in pregnant women with group B streptococ-
cal urinary infections or urinary antibodies to group B streptococcal and E.
coli antigens. Br. J. Obstet. Gynecol. 101:107–113.

11. Moller, M., A. C. Thomsen, K. Borch, K. Dinesen, and M. Zdravkovic. 1984.
Rupture of fetal membranes and premature delivery associated with group B
streptococci in urine of pregnant women. Lancet 2:69–70.

12. Nguyen, T. M., D. W. Gauthier, T. D. Mules, B. S. Nuwayhid, M. A. Viana,
and P. C. Schreckenberger. 1998. Detection of group B streptococcus: com-
parison of an optical immunoassay with direct plating and broth-enhanced
culture methods. J. Matern. Fetal Med. 7:172–176.

13. Ostroff, R. M., and J. W. Steaffens. 1995. Effect of specimen storage, anti-
biotics, and feminine hygiene products on the detection of group B strepto-
coccus by culture and the STREP B OIA test. Diagn. Microbiol. Infect. Dis.
22:253–259.

14. Park, C. H., D. Ruprai, N. M. Vandel, D. L. Hixon, and F. E. Mecklenburg.
1996. Rapid detection of group B streptococcal antigen from vaginal speci-
mens using a new optical immunoassay technique. Diagn. Microbiol. Infect.
Dis. 24:125–128.

15. Regan, J. A., S. Chao, and L. S. James. 1981. Premature rupture of mem-
branes, preterm delivery, and group B streptococcal colonization of mothers.
Am. J. Obstet. Gynecol. 141:184–186.

16. Regan, J. A., M. A. Klebanoff, R. P. Nugent, D. A. Eschenbach, W. C.
Blackwelder, Y. Lou, R. S. Gibbs, P. J. Rettig, D. H. Martin, and R. Edelman.
1996. Colonization with group B streptococci in pregnancy and adverse
outcome. Am. J. Obstet. Gynecol. 174:1354–1360.

17. Reisner, D. P., M. J. Haas, R. W. Zingheim, M. A. Williams, and D. A. Luthy.
2000. Performance of a group B streptococcal prophylaxis protocol combin-
ing high-risk treatment and low-risk screening. Am. J. Obstet. Gynecol.
182:1335–1343.

18. Samadi, R., A. Stek, and J. S. Greenspoon. 2001. Evaluation of a rapid
optical immunoassay-based test for group B streptococcus colonization in
intrapartum patients. J. Matern. Fetal Med. 10:203–208.

19. Song, J. Y., L. L. Lin, S. Shott, N. Kimber, J. Tangora, A. Cohen, A. Wells,
M. Maezes, A. Aroutcheva, and S. Faro. 1999. Evaluation of the Strep B OIA
test compared to standard culture methods for detection of group B strep-
tococci. Infect. Dis. Obstet. Gynecol. 7:202–205.

5290 NOTES J. CLIN. MICROBIOL.

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ttp

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/

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