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Perinatal screening for group B streptococci: cost-benefit analysis of rapid polymerase chain reaction |
Haberland C A, Benitz W E, Sanders G D, Pietzsch J B, Yamada S, Nguyen L, Garber A M |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Three strategies for screening for group B streptococci (GBS) in expectant mothers were examined:
screening mothers using rapid polymerase chain reaction (PCR) at time of admission for labour (PCR strategy);
use of the standard guidelines-recommended strategy of screening with 35- to 27-week culture (culture strategy); and
treatment based on the presence or absence of maternal risk factors at the time of labour (risk-factor strategy).
Study population The study population comprised a hypothetical cohort of expectant mothers delivering at term. Only term pregnancies in women without a prior history of GBS-infected infants were considered.
Setting The setting was likely to have been secondary care. The economic study was carried out in the USA.
Dates to which data relate The effectiveness data were derived from studies published between 1977 and 2001. No specific dates for resource use were reported. The price year was 2001.
Source of effectiveness data The effectiveness evidence was derived from a review of completed studies and authors' assumptions.
Modelling A decision tree model was constructed to compare the clinical and economic outcomes of the three alternative screening strategies in a hypothetical cohort of 1,000,000 births. Antibiotic treatment was decided on the basis of the test results. Infected infants were admitted to the neonatal intensive care unit (NICU). Possible infant outcomes were death, disability, or wellness. The model was deterministic and the tree structure was shown graphically in the paper.
Outcomes assessed in the review The outcomes derived from the literature were population risks, test characteristics, infection rates and clinical outcomes.
The parameters related to population risks were:
the prevalence of rectovaginal colonisation with GBS,
the prevalence of vaginal colonisation with GBS,
the probability of receiving adequate prenatal care, and
the probability of having risk factors during labour at term.
The test characteristics derived were the sensitivity and specificity of PCR and culture.
The parameters related to infection rates were:
the probability of infant infection given maternal GBS colonisation in the general tract at the time of labour, of infant infection given no maternal GBS colonisation in the genital tract at the time of labour,
the probability of infant infection given maternal risk factors,
the probability of infant infection given no maternal risk factors, and
the decrease in infant infection rate after maternal prophylaxis.
The parameters related to clinical outcomes were:
the probability of infant death after infection,
the probability of infant disability after infection, and
the probability of infant recovery and wellness after infection.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included The effectiveness data were derived from approximately 24 studies.
Methods of combining primary studies Investigation of differences between primary studies Results of the review The prevalence of rectovaginal colonisation with GBS was 22.8% (range: 18.2 - 27.4).
The prevalence of vaginal colonisation with GBS was 14.7% (range: 11.8 - 17.6).
The probability of receiving adequate prenatal care was 95% (range: 70 - 100).
The probability of having risk factors during labour at term was 7.65% (range: 6.05 - 9.07).
The sensitivity of PCR was 100% (range: 80 - 100) and the specificity was 98.9% (range: 80 - 100). The sensitivity of culture was 90.8% and the specificity was 88.9%.
The probability of infant infection given maternal GBS colonisation in the genital tract at the time of labour was 1.47% (range: 1.18 - 1.76).
The probability of infant infection given no maternal GBS colonisation in the genital tract at the time of labour was 0.0017% (range: 0.0013 - 0.002).
The probability of infant infection given maternal risk factors was 1.4% (range: 1.12 - 1.68).
The probability of infant infection given no maternal risk factors was 0.12% (range: 0.096 - 0.14).
The rate of decrease in infant infection rate after maternal prophylaxis was 80.2% (range: 70 - 86).
The probability of infant death after infection was 1% (range: 0 - 5).
The probability of infant disability after infection was 1.6% (range: 0 - 10).
The probability of infant recovery and wellness after infection was 97.4% (range: 90 - 100).
Methods used to derive estimates of effectiveness The authors made some assumptions that were used in the decision model.
Estimates of effectiveness and key assumptions It was assumed that each delivery would result in a singleton birth. In addition, all mothers with positive tests or positive risk factors would receive timely and appropriate antibiotics, and treatment would be dictated by the results of the testing.
Measure of benefits used in the economic analysis The child's potential lifetime earnings were used as the summary benefit measure in the cost-benefit analysis. The human capital approach was used. Such earnings were derived from the decision model and a discount rate of 3% was applied. Some outputs of the model were also reported. More specifically, the number of infant infections with GBS, the number of infant deaths attributable to GBS, and the number of infant disabilities attributable to GBS.
Direct costs A discount rate of 3% was applied as long-term costs were estimated in the model. The unit costs were only reported separately from the quantities of resources used for some items. The health services included in the economic evaluation were PCR tests, 35- to 37-week culture, maternal antibiotic prophylaxis, in-hospital care of non-infected infants, NICU care for GBS-infected infants, and the lifetime health care costs for a healthy or disabled infant. The cost/resource boundary of the study was that of society. The costs of treating the maternal outcomes of postpartum bacteraemia and endometritis were excluded since the analysis focused on infant costs. Resource use was mainly estimated from authors' assumptions and some published studies. The costs came from a single centre, local manufacturers and published costs. The price year was 2001.
Statistical analysis of costs The costs were not treated stochastically.
Indirect Costs The indirect costs were considered in the analysis as the monetary benefit used as the summary benefit measure in the cost-benefit analysis.
Sensitivity analysis One- and two-way sensitivity analyses were carried out to assess the robustness of the estimated benefits and costs to variations in key costs and most of the model inputs. The key costs were for PCR, maternal antibiotics, acute NICU care, in-hospital care for well infants, and long-term care for well and disabled children. The model inputs included potential lifetime income, the percentage of women receiving adequate perinatal care, PCR sensitivity and specificity, prevalence of GBS colonisation, prevalence of maternal risk factors, probability of GS illness, probability of infant death and disability, and infant infection rates after maternal prophylaxis. The ranges of values used were derived from the literature or were values +/- 20%.
Estimated benefits used in the economic analysis The estimated lifetime earnings were $411,186 with the risk-factor strategy, $411,193 with the culture strategy, and $411,195 with the PCR strategy.
In the hypothetical cohort of 1,000,000 births, the number of infant infections with GBS was 1,320 with the risk-factor strategy, 654 with the culture strategy, and 436 with the PCR strategy.
The number of infant deaths attributable to GBS was 13 with the risk-factor strategy, 7 with the culture strategy, and 4 with the PCR strategy.
The number of infant disabilities attributable to GBS was 21 with the risk-factor strategy, 10 with the culture strategy, and 7 with the PCR strategy.
Cost results The estimated lifetime costs were $34,448 with the risk-factor strategy, $34,454 with the culture strategy, and $34,450 with the PCR strategy.
Synthesis of costs and benefits In the cost-benefit approach, the costs and benefits were combined by calculating the expected societal benefit. This was the difference between the present values of earnings (benefit measure) and the direct lifetime costs. Earnings lost because of death or disability were also considered in the analysis. The study results showed that the net present value of earning minus the net present value of direct costs was $376,738 with the risk-factor strategy, $376,739 with the culture strategy, and $376,745 with the PCR strategy. The PCR strategy led to a gain of only $7 relative to the risk-factor strategy and of only $6 in comparison with the culture strategy. Therefore, the differences in the monetary benefits were small.
The sensitivity analysis revealed that, when comparing the PCR and risk-factor strategies, the estimated net societal benefits were sensitive to variations in the NICU costs, probability of disability, and the cost of PCR. When comparing the PCR and culture strategies, the key factors were the cost of the PCR test, NICU costs, and the sensitivity of PCR. However, other than at the extreme ranges for the most influential variables, the PCR strategy provided greater net benefits than the other two strategies.
Authors' conclusions The polymerase chain reaction (PCR) test strategy led to greater net benefits than the risk-factor and the 35- to 37-week culture strategies, although the differences were small.
CRD COMMENTARY - Selection of comparators The authors provided a clear explanation for the choice of the comparators that were used in the study. Both the risk-factor strategy and the 35- to 37-week culture strategy represented currently recommended approaches, while the PCR strategy was a new intervention. You should decide whether they are valid comparators in your own setting.
Validity of estimate of measure of effectiveness The effectiveness data used to populate the decision model were mainly derived from published studies. However, it was unclear whether a systematic review of the literature had been carried out. In addition, no information on the primary studies (such as design, patient sample and size of the groups) was provided. It is therefore difficult to assess the quality of the sources used. Further, the methods used to combine the primary studies were not reported. The authors also made assumptions, but uncertainty around such estimates was not investigated in the sensitivity analysis. Given the lack of reporting on these issues it is difficult to judge the overall quality of the effectiveness data.
Validity of estimate of measure of benefit The monetary benefits associated with the screening interventions were used as the summary benefits. This choice was appropriate within the framework of the cost-benefit analysis. Discounting was relevant as the lifetime benefits were estimated, and it was appropriately carried out. The human capital approach was used to estimate the value of a human life. This represents a widely used method.
Validity of estimate of costs The analysis of the costs was carried out consistently with the perspective adopted, as the indirect costs were estimated on the benefit side due to the cost-benefit design. The price year was reported, therefore facilitating reflation exercises in other settings. Discounting was appropriately carried out. The source of the cost data was reported for all cost items. However, information on resource use was scarce. Such information was generally based on authors' assumptions for which no explicit justification was provided, but which presumably reflected standard patterns of care. The whole analysis was carried out deterministically.
Other issues The authors did not compare their findings with those from other published studies. In terms of the issue of the generalisability of the study results to other settings, the authors stated that the conclusions of the study were likely to refer to large hospitals with an on-site and capable laboratory within the same hospital. Therefore, due to the high pre-test costs, PCR would be a less attractive option for lower-volume hospitals. The authors noted some limitations to the validity of the study. First, some of the estimates used in the decision model were sparse and came from different studies. Second, variations in cost might be observed in practice in the real world. Third, the timely administration of antibiotics represents a critical variable for the success of each strategy. The authors also noted that the inclusion of parental disutilities and lost parental income would have increased the overall societal value of PCR.
Implications of the study The main implication of the study was that PCR represents a promising approach for the identification of mothers with GBS. The authors suggested that further studies should investigate the rate at which antibiotics can be delivered quickly and effectively, as this might improve the success of all screening strategies for GBS.
Source of funding Supported by the Homer Laughlin Endowment at the Center for Primary Care and Outcomes Research.
Bibliographic details Haberland C A, Benitz W E, Sanders G D, Pietzsch J B, Yamada S, Nguyen L, Garber A M. Perinatal screening for group B streptococci: cost-benefit analysis of rapid polymerase chain reaction. Pediatrics 2002; 110(3): 471-480 Indexing Status Subject indexing assigned by NLM MeSH Cost-Benefit Analysis; Decision Trees; Delivery, Obstetric; Female; Humans; Infant, Newborn; Labor, Obstetric; Mass Screening /economics /methods; Polymerase Chain Reaction /economics /methods; Predictive Value of Tests; Pregnancy; Pregnancy Complications, Infectious /diagnosis /economics /prevention & Sensitivity and Specificity; Streptococcal Infections /diagnosis /economics /prevention & Streptococcus agalactiae /isolation & control; control; purification AccessionNumber 22002001575 Date bibliographic record published 30/11/2004 Date abstract record published 30/11/2004 |
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