Group B streptococcal infection screening: Difference between revisions
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==Overview== | ==Overview== | ||
CDC's screening guidelines for Group B streptococcal (GBS) infection recommend universal culture-based screening for '''all pregnant women''' for vaginal and rectal GBS colonization (class A, level of evidence II) in order to determine which women should receive intrapartum GBS chemoprophylaxis. CDC recommended that women with unknown GBS colonization status at the time of delivery be managed according to the presence of intrapartum risk factors. CDC's guidelines recommend screening for '''vaginal''' and '''rectal''' GBS colonization at '''35-37 weeks' gestation'''. Swabbing both the lower [[vagina]] and [[rectum]] (through the [[anal sphincter]]) increases the culture yield substantially compared with sampling the [[cervix]] or the vagina without also swabbing the rectum.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | |||
==Screening== | ==Screening== | ||
===Indications=== | ===Indications=== | ||
CDC's guidelines recommend universal culture-based screening for '''all pregnant women''' for vaginal and rectal GBS colonization (class A, level of evidence II) to determine which women should receive intrapartum GBS chemoprophylaxis. CDC recommended that women with unknown GBS colonization status at the time of delivery be managed according to the presence of intrapartum risk factors. | CDC's guidelines recommend universal culture-based screening for '''all pregnant women''' for vaginal and rectal GBS colonization (class A, level of evidence II) in order to determine which women should receive intrapartum GBS chemoprophylaxis. CDC recommended that women with unknown GBS colonization status at the time of delivery be managed according to the presence of intrapartum risk factors.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
===Timing=== | ===Timing=== | ||
CDC's guidelines recommend screening for '''vaginal''' and '''rectal''' GBS colonization at '''35-37 weeks' gestation'''. | CDC's guidelines recommend screening for '''vaginal''' and '''rectal''' GBS colonization at '''35-37 weeks' gestation'''.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
===Culture- Versus Risk-Based Screening=== | ===Culture- Versus Risk-Based Screening=== | ||
Early guidelines recommended the use of one of two approaches to identifying women who should receive intrapartum antibiotic prophylaxis: a risk-based approach or a culture-based screening approach.<ref name=CDC1996>CDC. Prevention of perinatal group B streptococcal disease: a public health perspective. MMWR 1996;45(No. RR-7).[http://www.cdc.gov/mmwr/preview/mmwrhtml/00043277.htm]</ref> A large population-based study conducted during 1998--1999 demonstrated the superiority of culture-based screening over the risk-based approach to prevention of early-onset GBS disease.<ref name="pmid12140298">{{cite journal| author=Schrag SJ, Zell ER, Lynfield R, Roome A, Arnold KE, Craig AS et al.| title=A population-based comparison of strategies to prevent early-onset group B streptococcal disease in neonates. | journal=N Engl J Med | year= 2002 | volume= 347 | issue= 4 | pages= 233-9 | pmid=12140298 | doi=10.1056/NEJMoa020205 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12140298 }} </ref> The study found that culture-based screening resulted in the identification of a greater proportion of women at risk for transmitting GBS to their newborns. | Early guidelines recommended the use of one of two approaches to identifying women who should receive intrapartum antibiotic prophylaxis: a risk-based approach or a culture-based screening approach.<ref name=CDC1996>CDC. Prevention of perinatal group B streptococcal disease: a public health perspective. MMWR 1996;45(No. RR-7).[http://www.cdc.gov/mmwr/preview/mmwrhtml/00043277.htm]</ref> A large population-based study conducted during 1998--1999 demonstrated the superiority of culture-based screening over the risk-based approach to prevention of early-onset GBS disease.<ref name="pmid12140298">{{cite journal| author=Schrag SJ, Zell ER, Lynfield R, Roome A, Arnold KE, Craig AS et al.| title=A population-based comparison of strategies to prevent early-onset group B streptococcal disease in neonates. | journal=N Engl J Med | year= 2002 | volume= 347 | issue= 4 | pages= 233-9 | pmid=12140298 | doi=10.1056/NEJMoa020205 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12140298 }} </ref> The study found that culture-based screening resulted in the identification of a greater proportion of women at risk for transmitting GBS to their newborns.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
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Studies have indicated that when women in the outpatient clinic setting collect their own vaginal-rectal screening specimens, with appropriate instruction, GBS yield is similar to when specimens are collected by a health-care provider. | Studies have indicated that when women in the outpatient clinic setting collect their own vaginal-rectal screening specimens, with appropriate instruction, GBS yield is similar to when specimens are collected by a health-care provider. | ||
The use of appropriate transport media can help sustain the viability of GBS in settings where immediate laboratory processing is not possible. GBS isolates can remain viable in transport media for several days at room temperature; however, the recovery of isolates declines during 1-4 days, particularly at high temperatures. Even when appropriate transport media are used, the [[sensitivity]] of culture is greatest when the specimen is stored at 4°C before culture and processed within 24 hours of collection. | The use of appropriate transport media can help sustain the viability of GBS in settings where immediate laboratory processing is not possible. GBS isolates can remain viable in transport media for several days at room temperature; however, the recovery of isolates declines during 1-4 days, particularly at high temperatures. Even when appropriate transport media are used, the [[sensitivity]] of culture is greatest when the specimen is stored at 4°C before culture and processed within 24 hours of collection.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
====Specimen Processing==== | ====Specimen Processing==== | ||
Regardless of the test selected to identify GBS, use of an enrichment broth improves detection substantially. When direct agar plating is used instead of selective enrichment broth, as many as 50% of women who are GBS carriers have false-negative culture results. Examples of selective enrichment broths include Todd-Hewitt broth supplemented either with [[gentamicin]] (8 µg/ml) and [[nalidixic acid]] (15 µg/ml) [TransVag broth] or with [[colistin]] (10 µg/ml) and [[nalidixic acid]] (15 µg/ml) [Lim broth]. Although TransVag and Lim broth media are often available without blood, the addition of 5% sheep blood can increase the recovery of GBS . Selective enrichment broth also can contain chromogenic substrates that provide for a change in color in the setting of beta-hemolytic GBS. Such broths can facilitate the identification of beta-hemolytic GBS; however, non-hemolytic isolates will not be detected by these broths alone. | Regardless of the test selected to identify GBS, use of an enrichment broth improves detection substantially. When direct agar plating is used instead of selective enrichment broth, as many as 50% of women who are GBS carriers have false-negative culture results. Examples of selective enrichment broths include Todd-Hewitt broth supplemented either with [[gentamicin]] (8 µg/ml) and [[nalidixic acid]] (15 µg/ml) [TransVag broth] or with [[colistin]] (10 µg/ml) and [[nalidixic acid]] (15 µg/ml) [Lim broth]. Although TransVag and Lim broth media are often available without blood, the addition of 5% sheep blood can increase the recovery of GBS . Selective enrichment broth also can contain chromogenic substrates that provide for a change in color in the setting of beta-hemolytic GBS. Such broths can facilitate the identification of beta-hemolytic GBS; however, non-hemolytic isolates will not be detected by these broths alone.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
Following enrichment, the conventional means for identifying GBS is through isolation on subculture to blood agar plates and presumptive identification by the CAMP test or serologic identification using | Following enrichment, the conventional means for identifying GBS is through isolation on subculture to blood agar plates and presumptive identification by the CAMP test or serologic identification using latex agglutination with group B streptococcal antisera. More recently, chromogenic agars that undergo color change in the presence of beta-hemolytic colonies of GBS have become available. As with pigmented enrichment broths, these chromogenic agars can facilitate detection of beta-hemolytic GBS, but the majority will not detect non-hemolytic strains. In addition more rapid techniques for identifying GBS directly from enrichment broth, or after subculture have been developed, including [[DNA]] probes and nucleic acid amplification tests (NAAT) such as [[polymerase chain reaction]].<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
Despite the availability of NAAT for GBS, utility of such assays in the intrapartum setting remains limited. Although a highly sensitive and specific test with rapid turnaround time could be used to assess intrapartum GBS colonization and therefore obviate the need for antenatal screening, data on currently available assays do not support their use in replacement of antenatal culture or risk-based assessment of women with unknown GBS status on admission for labor. The additional time required for enrichment of samples makes it not feasible for intrapartum testing, and the [[sensitivity]] of assays in the absence of enrichment is not adequate in comparison to culture. In addition, concerns remain regarding real-world turnaround time, test complexity, availability of testing at all times, staffing requirements, and costs. In settings that can perform NAAT, such tests might prove useful for the limited circumstance of a woman at term with unknown colonization status and no other risk factors. Even optimal NAAT would have drawbacks in the intrapartum setting, including a delay in administration of [[antibiotics]] while waiting for the result, and no antimicrobial susceptibility testing for [[penicillin]]-allergic women. Other rapid tests in addition to NAAT have been developed to detect GBS rapidly from non-enriched samples, including optical immunoassays and [[enzyme immunoassay]]s; however, none is sufficiently sensitive when used on a direct specimen to detect GBS colonization reliably in the intrapartum setting. | Despite the availability of NAAT for GBS, utility of such assays in the intrapartum setting remains limited. Although a highly sensitive and specific test with rapid turnaround time could be used to assess intrapartum GBS colonization and therefore obviate the need for antenatal screening, data on currently available assays do not support their use in replacement of antenatal culture or risk-based assessment of women with unknown GBS status on admission for labor. The additional time required for enrichment of samples makes it not feasible for intrapartum testing, and the [[sensitivity]] of assays in the absence of enrichment is not adequate in comparison to culture. In addition, concerns remain regarding real-world turnaround time, test complexity, availability of testing at all times, staffing requirements, and costs. In settings that can perform NAAT, such tests might prove useful for the limited circumstance of a woman at term with unknown colonization status and no other risk factors. Even optimal NAAT would have drawbacks in the intrapartum setting, including a delay in administration of [[antibiotics]] while waiting for the result, and no antimicrobial susceptibility testing for [[penicillin]]-allergic women. Other rapid tests in addition to NAAT have been developed to detect GBS rapidly from non-enriched samples, including optical immunoassays and [[enzyme immunoassay]]s; however, none is sufficiently sensitive when used on a direct specimen to detect GBS colonization reliably in the intrapartum setting.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
====Antimicrobial Susceptibility Testing==== | ====Antimicrobial Susceptibility Testing==== | ||
Antimicrobial susceptibility testing of GBS isolates is crucial for appropriate antibiotic prophylaxis selection for [[penicillin]]-allergic women who are at high risk for anaphylaxis because resistance to [[clindamycin]], the most common agent used in this population, is increasing among GBS isolates. | Antimicrobial susceptibility testing of GBS isolates is crucial for appropriate antibiotic prophylaxis selection for [[penicillin]]-allergic women who are at high risk for anaphylaxis because resistance to [[clindamycin]], the most common agent used in this population, is increasing among GBS isolates.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
In addition, appropriate methodologies for susceptibility testing are important because inducible [[clindamycin]] resistance can occur in some strains that appear susceptible in broth susceptibility tests. D-zone testing using the double-disk diffusion method has been used to identify isolates that are [[erythromycin]]-resistant and [[clindamycin]]-susceptible, yet have inducible resistance to [[clindamycin]]. Isolates that are D-zone positive are considered to have inducible [[clindamycin]] resistance and are presumed to be resistant although the clinical significance of this resistance is not clear. | In addition, appropriate methodologies for susceptibility testing are important because inducible [[clindamycin]] resistance can occur in some strains that appear susceptible in broth susceptibility tests. D-zone testing using the double-disk diffusion method has been used to identify isolates that are [[erythromycin]]-resistant and [[clindamycin]]-susceptible, yet have inducible resistance to [[clindamycin]]. Isolates that are D-zone positive are considered to have inducible [[clindamycin]] resistance and are presumed to be resistant although the clinical significance of this resistance is not clear.<ref name=CDCMMWR>Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_w CDC.gov]</ref> | ||
==References== | ==References== | ||
Revision as of 20:24, 19 August 2014
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Group B Streptococcal Infection Microchapters |
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Differentiating Group B Streptococcal Infection from other Diseases |
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Group B streptococcal infection screening On the Web |
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Risk calculators and risk factors for Group B streptococcal infection screening |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [3]
Overview
CDC's screening guidelines for Group B streptococcal (GBS) infection recommend universal culture-based screening for all pregnant women for vaginal and rectal GBS colonization (class A, level of evidence II) in order to determine which women should receive intrapartum GBS chemoprophylaxis. CDC recommended that women with unknown GBS colonization status at the time of delivery be managed according to the presence of intrapartum risk factors. CDC's guidelines recommend screening for vaginal and rectal GBS colonization at 35-37 weeks' gestation. Swabbing both the lower vagina and rectum (through the anal sphincter) increases the culture yield substantially compared with sampling the cervix or the vagina without also swabbing the rectum.[1]
Screening
Indications
CDC's guidelines recommend universal culture-based screening for all pregnant women for vaginal and rectal GBS colonization (class A, level of evidence II) in order to determine which women should receive intrapartum GBS chemoprophylaxis. CDC recommended that women with unknown GBS colonization status at the time of delivery be managed according to the presence of intrapartum risk factors.[1]
Timing
CDC's guidelines recommend screening for vaginal and rectal GBS colonization at 35-37 weeks' gestation.[1]
Culture- Versus Risk-Based Screening
Early guidelines recommended the use of one of two approaches to identifying women who should receive intrapartum antibiotic prophylaxis: a risk-based approach or a culture-based screening approach.[2] A large population-based study conducted during 1998--1999 demonstrated the superiority of culture-based screening over the risk-based approach to prevention of early-onset GBS disease.[3] The study found that culture-based screening resulted in the identification of a greater proportion of women at risk for transmitting GBS to their newborns.[1]
| Risk-Based Method | Culture-Based Method |
Presence of any of the following intrapartum risk factors:
|
All pregnant women between 35 and 37 week's gestation undergo culture searching for:
|
Specimen Collection and Processing for GBS Screening
Specimen Collection
Swabbing both the lower vagina and rectum (through the anal sphincter) increases the culture yield substantially compared with sampling the cervix or the vagina without also swabbing the rectum.
Although a small number of studies have examined the ability of perianal or vaginal-perianal cultures to detect GBS colonization, the available data on their performance compared with vaginal-rectal cultures are limited.
Studies have indicated that when women in the outpatient clinic setting collect their own vaginal-rectal screening specimens, with appropriate instruction, GBS yield is similar to when specimens are collected by a health-care provider.
The use of appropriate transport media can help sustain the viability of GBS in settings where immediate laboratory processing is not possible. GBS isolates can remain viable in transport media for several days at room temperature; however, the recovery of isolates declines during 1-4 days, particularly at high temperatures. Even when appropriate transport media are used, the sensitivity of culture is greatest when the specimen is stored at 4°C before culture and processed within 24 hours of collection.[1]
Specimen Processing
Regardless of the test selected to identify GBS, use of an enrichment broth improves detection substantially. When direct agar plating is used instead of selective enrichment broth, as many as 50% of women who are GBS carriers have false-negative culture results. Examples of selective enrichment broths include Todd-Hewitt broth supplemented either with gentamicin (8 µg/ml) and nalidixic acid (15 µg/ml) [TransVag broth] or with colistin (10 µg/ml) and nalidixic acid (15 µg/ml) [Lim broth]. Although TransVag and Lim broth media are often available without blood, the addition of 5% sheep blood can increase the recovery of GBS . Selective enrichment broth also can contain chromogenic substrates that provide for a change in color in the setting of beta-hemolytic GBS. Such broths can facilitate the identification of beta-hemolytic GBS; however, non-hemolytic isolates will not be detected by these broths alone.[1]
Following enrichment, the conventional means for identifying GBS is through isolation on subculture to blood agar plates and presumptive identification by the CAMP test or serologic identification using latex agglutination with group B streptococcal antisera. More recently, chromogenic agars that undergo color change in the presence of beta-hemolytic colonies of GBS have become available. As with pigmented enrichment broths, these chromogenic agars can facilitate detection of beta-hemolytic GBS, but the majority will not detect non-hemolytic strains. In addition more rapid techniques for identifying GBS directly from enrichment broth, or after subculture have been developed, including DNA probes and nucleic acid amplification tests (NAAT) such as polymerase chain reaction.[1]
Despite the availability of NAAT for GBS, utility of such assays in the intrapartum setting remains limited. Although a highly sensitive and specific test with rapid turnaround time could be used to assess intrapartum GBS colonization and therefore obviate the need for antenatal screening, data on currently available assays do not support their use in replacement of antenatal culture or risk-based assessment of women with unknown GBS status on admission for labor. The additional time required for enrichment of samples makes it not feasible for intrapartum testing, and the sensitivity of assays in the absence of enrichment is not adequate in comparison to culture. In addition, concerns remain regarding real-world turnaround time, test complexity, availability of testing at all times, staffing requirements, and costs. In settings that can perform NAAT, such tests might prove useful for the limited circumstance of a woman at term with unknown colonization status and no other risk factors. Even optimal NAAT would have drawbacks in the intrapartum setting, including a delay in administration of antibiotics while waiting for the result, and no antimicrobial susceptibility testing for penicillin-allergic women. Other rapid tests in addition to NAAT have been developed to detect GBS rapidly from non-enriched samples, including optical immunoassays and enzyme immunoassays; however, none is sufficiently sensitive when used on a direct specimen to detect GBS colonization reliably in the intrapartum setting.[1]
Antimicrobial Susceptibility Testing
Antimicrobial susceptibility testing of GBS isolates is crucial for appropriate antibiotic prophylaxis selection for penicillin-allergic women who are at high risk for anaphylaxis because resistance to clindamycin, the most common agent used in this population, is increasing among GBS isolates.[1]
In addition, appropriate methodologies for susceptibility testing are important because inducible clindamycin resistance can occur in some strains that appear susceptible in broth susceptibility tests. D-zone testing using the double-disk diffusion method has been used to identify isolates that are erythromycin-resistant and clindamycin-susceptible, yet have inducible resistance to clindamycin. Isolates that are D-zone positive are considered to have inducible clindamycin resistance and are presumed to be resistant although the clinical significance of this resistance is not clear.[1]
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Verani J.R., McGee L, and Schrag S.J. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010.CDC.gov
- ↑ CDC. Prevention of perinatal group B streptococcal disease: a public health perspective. MMWR 1996;45(No. RR-7).[1]
- ↑ Schrag SJ, Zell ER, Lynfield R, Roome A, Arnold KE, Craig AS; et al. (2002). "A population-based comparison of strategies to prevent early-onset group B streptococcal disease in neonates". N Engl J Med. 347 (4): 233–9. doi:10.1056/NEJMoa020205. PMID 12140298.