Quality Assurance Sampling Research Articles

Effect of Decision Rules for Lot Quality Assurance Sampling on an Assessment of Micronutrient Program Coverage

Lot quality assurance sampling (LQAS) is a sampling method that assesses small areas to determine if key goals of public health programs have been met. LQAS was used to monitor a new micronutrient powder (MNP) distribution program in Country X. LQAS decision rules (DR) were used to classify districts as having adequate or inadequate coverage with respect to three criteria: goal coverage, the lower limit of acceptable coverage, and the coverage level above which further intervention was not cost‐effective. There is controversy in recent literature between two approaches to DR selection: the first balances coverage goals with program expense, while the second prioritizes detection of low‐coverage districts. This study compared results from both approaches to DR selection. In each of 48 districts, 24 households were randomly selected. Goal district coverage for MNP use was 70%. Using the first approach, a DR of 16 households (66.7% of each district sample) defined adequate coverage. Using the second approach, a DR of 20 (83.3%) was used. DRs were selected using FANTA‐II software. Using the first DR, coverage was inadequate in 14.6% of districts, compared to 47.9% using the second DR. Choice of DR substantially altered the number of districts in need of more resources to improve coverage. The first approach allows this new program with limited resources to focus on the worst‐performing districts. The second approach ensures that passing districts have met the coverage goal and is useful once a minimal effective level of coverage is determined. The key to DR selection is examination of the current needs of each program.

Multidrug Resistance Among New Tuberculosis Cases

Current methodology for multidrug-resistant tuberculosis (MDR TB) surveys endorsed by the World Health Organization provides estimates of MDR TB prevalence among new cases at the national level. On the aggregate, local variation in the burden of MDR TB may be masked. This paper investigates the utility of applying lot quality-assurance sampling to identify geographic heterogeneity in the proportion of new cases with multidrug resistance. We simulated the performance of lot quality-assurance sampling by applying these classification-based approaches to data collected in the most recent TB drug-resistance surveys in Ukraine, Vietnam, and Tanzania. We explored 3 classification systems- two-way static, three-way static, and three-way truncated sequential sampling-at 2 sets of thresholds: low MDR TB = 2%, high MDR TB = 10%, and low MDR TB = 5%, high MDR TB = 20%. The lot quality-assurance sampling systems identified local variability in the prevalence of multidrug resistance in both high-resistance (Ukraine) and low-resistance settings (Vietnam). In Tanzania, prevalence was uniformly low, and the lot quality-assurance sampling approach did not reveal variability. The three-way classification systems provide additional information, but sample sizes may not be obtainable in some settings. New rapid drug-sensitivity testing methods may allow truncated sequential sampling designs and early stopping within static designs, producing even greater efficiency gains. Lot quality-assurance sampling study designs may offer an efficient approach for collecting critical information on local variability in the burden of multidrug-resistant TB. Before this methodology is adopted, programs must determine appropriate classification thresholds, the most useful classification system, and appropriate weighting if unbiased national estimates are also desired.

Whom and where are we not vaccinating? Coverage after the introduction of a new conjugate vaccine against group A meningococcus in Niger in 2010.

MenAfriVac is a new conjugate vaccine against Neisseria meningitidis serogroup A developed for the African “meningitis belt”. In Niger, the first two phases of the MenAfriVac introduction campaign were conducted targeting 3,135,942 individuals aged 1 to 29 years in the regions of Tillabéri, Niamey, and Dosso, in September and December 2010. We evaluated the campaign and determined which sub-populations or areas had low levels of vaccination coverage in the regions of Tillabéri and Niamey. After Phase I, conducted in the Filingué district, we estimated coverage using a 30×15 cluster-sampling survey and nested lot quality assurance (LQA) analysis in the clustered samples to identify which subpopulations (defined by age 1–14/15–29 and sex) had unacceptable vaccination coverage (<70%). After Phase II, we used Clustered Lot Quality Assurance Sampling (CLQAS) to assess if any of eight districts in Niamey and Tillabéri had unacceptable vaccination coverage (<75%) and estimated overall coverage. Estimated vaccination coverage was 77.4% (95%CI: 84.6–70.2) as documented by vaccination cards and 85.5% (95% CI: 79.7–91.2) considering verbal history of vaccination for Phase I; 81.5% (95%CI: 86.1–77.0) by card and 93.4% (95% CI: 91.0–95.9) by verbal history for Phase II. Based on vaccination cards, in Filingué, we identified both the male and female adult (age 15–29) subpopulations as not reaching 70% coverage; and we identified three (one in Tillabéri and two in Niamey) out of eight districts as not reaching 75% coverage confirmed by card. Combined use of LQA and cluster sampling was useful to estimate vaccination coverage and to identify pockets with unacceptable levels of coverage (adult population and three districts). Although overall vaccination coverage was satisfactory, we recommend continuing vaccination in the areas or sub-populations with low coverage and reinforcing the social mobilization of the adult population.

Outbreak response immunisation: the experience of Chad during recurrent measles epidemics in 2005 and 2010

Despite impressive gains in measles control globally, measles epidemics continue to occur in countries with insufficient vaccination coverage. WHO guidelines now recommend outbreak response immunisation (ORI) for controlling measles outbreaks in certain contexts. The objective of this study was to describe late and early response vaccination activities during two consecutive measles outbreaks that occurred in 2005 and 2010 in N'Djamena, Chad. Using Lot Quality Assurance Sampling, vaccination coverage was estimated to be low before the interventions. Following mass vaccination campaigns, measles cases declined. The timeliness and quality of ORI activities are crucial determinants of success. However, effective outbreak response should be accompanied by strong routine vaccination programmes to ensure sustainable high vaccination coverage.

Two Years of Follow-Up Validates the Echocardiographic Criteria for the Diagnosis and Screening of Rheumatic Heart Disease in Asymptomatic Populations

Out of 1,059 school children aged 6-15 years, screened 2 years ago, 54 children were diagnosed with rheumatic heart disease (RHD) and put on penicillin prophylaxis. Significant regurgitation of mitral valves was detected in 39 cases of echocardiography diagnosed RHD, and in 15 cases significant regurgitation was detected to coexist with valve deformities. Three children had isolated mitral valve thickening without regurgitation. They were not given penicillin prophylaxis. These cases were followed up for 2 years. After 2 years, 54 children diagnosed with RHD and three children with isolated mitral valve thickening, were evaluated again. Lot quality assurance sampling was employed to screen a selected group of school children declared normal during the earlier evaluation. Lot was to be rejected, if, one child with significant regurgitation of mitral valve was found among the first 10 screened children of each of the 10 lots. No lot was rejected and thus it was inferred that the prevalence of new onset RHD was negligible in the subset declared normal 2 years ago. Isolated significant mitral regurgitation disappeared more often when present (35.9%) in comparison to when it (26.7%) was originally found coexistent with valve deformities. Highlight of the study is the greater reversibility of earlier lesions as compared to the later stages of RHD. Spontaneous regression of isolated mitral valve thickening in two-thirds of the cases even without antibiotic prophylaxis, undermines the value of morphological criteria for the diagnosis of RHD.

Planning schistosomiasis control: investigation of alternative sampling strategies for Schistosoma mansoni to target mass drug administration of praziquantel in East Africa

In schistosomiasis control, there is a need to geographically target treatment to populations at high risk of morbidity. This paper evaluates alternative sampling strategies for surveys of Schistosoma mansoni to target mass drug administration in Kenya and Ethiopia. Two main designs are considered: lot quality assurance sampling (LQAS) of children from all schools; and a geostatistical design that samples a subset of schools and uses semi-variogram analysis and spatial interpolation to predict prevalence in the remaining unsurveyed schools. Computerized simulations are used to investigate the performance of sampling strategies in correctly classifying schools according to treatment needs and their cost-effectiveness in identifying high prevalence schools. LQAS performs better than geostatistical sampling in correctly classifying schools, but at a cost with a higher cost per high prevalence school correctly classified. It is suggested that the optimal surveying strategy for S. mansoni needs to take into account the goals of the control programme and the financial and drug resources available.

P1-45 Novel application of lot quality assurance sampling: as a quality control tool in census verification

IntroductionLot Quality Assurance Sampling (LQAS) was developed as technique for quality assurance in industrial production. The use of LQAS in health sciences is limited to coverage evaluations of different health...

SP4-39 Nutritional Vigilance System of Community: a lot quality assurance sampling for monitoring coverage of a nutritional knowledge and attitudes clues from mothers of children 0 to 23 months of age in Bolivia

BackgroundThis study reports on the results of a largescale targeted of nutritional promotional interventions in Bolivian municipalities with high Food Insecurity and Vulnerability classification.MethodsThe lot quality assurance sampling (LQAS) method...

Changes in the distribution of human schistosomiasis in Far North province, Cameroon, since 1986

Changes in the distribution of human schistosomiasis in Far North province, Cameroon, since 1986

Clustered lot quality assurance sampling: a pragmatic tool for timely assessment of vaccination coverage

To evaluate oral poliovirus vaccine (OPV) coverage of the November 2009 round in five Northern Nigeria states with ongoing wild poliovirus transmission using clustered lot quality assurance sampling (CLQAS). We selected four local government areas in each pre-selected state and sampled six clusters of 10 children in each Local Government Area, defined as the lot area. We used three decision thresholds to classify OPV coverage: 75-90%, 55-70% and 35-50%. A full lot was completed, but we also assessed in retrospect the potential time-saving benefits of stopping sampling when a lot had been classified. We accepted two local government areas (LGAs) with vaccination coverage above 75%. Of the remaining 18 rejected LGAs, 11 also failed to reach 70% coverage, of which four also failed to reach 50%. The average time taken to complete a lot was 10 h. By stopping sampling when a decision was reached, we could have classified lots in 5.3, 7.7 and 7.3 h on average at the 90%, 70% and 50% coverage targets, respectively. Clustered lot quality assurance sampling was feasible and useful to estimate OPV coverage in Northern Nigeria. The multi-threshold approach provided useful information on the variation of IPD vaccination coverage. CLQAS is a very timely tool, allowing corrective actions to be directly taken in insufficiently covered areas.

Clustered lot quality assurance sampling: a tool to monitor immunization coverage rapidly during a national yellow fever and polio vaccination campaign in Cameroon, May 2009

We used the clustered lot quality assurance sampling (clustered-LQAS) technique to identify districts with low immunization coverage and guide mop-up actions during the last 4 days of a combined oral polio vaccine (OPV) and yellow fever (YF) vaccination campaign conducted in Cameroon in May 2009. We monitored 17 pre-selected districts at risk for low coverage. We designed LQAS plans to reject districts with YF vaccination coverage <90% and with OPV coverage <95%. In each lot the sample size was 50 (five clusters of 10) with decision values of 3 for assessing OPV and 7 for YF coverage. We 'rejected' 10 districts for low YF coverage and 14 for low OPV coverage. Hence we recommended a 2-day extension of the campaign. Clustered-LQAS proved to be useful in guiding the campaign vaccination strategy before the completion of the operations.

Evaluation Of Immunization Coverage By Lot Quality Assurance Sampling In A Primary Health Center Area

Evaluation Of Immunization Coverage By Lot Quality Assurance Sampling In A Primary Health Center Area

X-ray fluorescence detection of waste engine oil residue in asphalt and its effect on cracking in service

This paper documents the discovery of waste engine oil residues in pavements across Ontario, Canada. We have found that recovered asphalts from a large majority of poorly performing contracts test positive for zinc through X-ray fluorescence (XRF) analysis. In contrast, neither the aggregates nor any of the well-performing asphalts showed any signs of the metal. Since zinc dialkyldithiophosphates are universal additives in engine oils, we inferred that the use of waste oil residues in asphalt must be widespread. Further analysis of 2008 quality assurance samples taken for the Ontario Ministry of Transportation substantiated this, with most samples testing positive for zinc. XRF analysis of straight waste oil residues suggests that typical modification levels are in the 5–20% range. The damaging effect of this additive through increased physical and chemical hardening is briefly discussed with reference to previous studies on unexplained, premature and excessive thermal cracking.

Absence of lymphatic filariasis infection among secondary-school children in Oman

The endemicity status of lymphatic filariasis in Oman is uncertain, with only sporadic cases reported, mostly imported. Immunochromatographic card test surveys were carried out to assess the presence of circulating Wuchereria bancrofti antigenaemia as a marker for active infection in children from suspected high-risk areas of Oman (South Batinah and Dhofar). Lot quality assurance sampling surveys were carried out on a minimum of 250 secondary-school children aged 17-18 years in each of 8 districts from February 2004 to March 2004. All tested students were negative for circulating W. bancrofti antigen. Based on these findings as well as previous data, Oman may possibly be classified as a nonendemic country, with no evidence of indigenous lymphatic filariasis transmission.

Diagnostic Accuracy and Feasibility of Serological Tests on Filter Paper Samples for Outbreak Detection of T.b. gambiense Human African Trypanosomiasis

Control of human African trypanosomiasis (HAT) in the Democratic Republic of Congo is based on mass population screening by mobile teams; a costly and labor-intensive approach. We hypothesized that blood samples collected on filter paper by village health workers and processed in a central laboratory might be a cost-effective alternative. We estimated sensitivity and specificity of micro-card agglutination test for trypanosomiasis (micro-CATT) and enzyme-linked immunosorbent assay (ELISA)/T.b. gambiense on filter paper samples compared with parasitology-based case classification and used the results in a Monte Carlo simulation of a lot quality assurance sampling (LQAS) approach. Micro-CATT and ELISA/T.b. gambiense showed acceptable sensitivity (92.7% [95% CI 87.4-98.0%] and 82.2% [95% CI 75.3-90.4%]) and very high specificity (99.4% [95% CI 99.0-99.9%] and 99.8% [95% CI 99.5-100%]), respectively. Conditional on high sample size per lot (> or = 60%), both tests could reliably distinguish a 2% from a zero prevalence at village level. Alternatively, these tests could be used to identify individual HAT suspects for subsequent confirmation.

Rapid appraisal of human intestinal helminth infections among schoolchildren in Osh oblast, Kyrgyzstan

A population-representative lot quality assurance sampling (LQAS) survey was conducted in 2009 to determine the prevalence of intestinal helminth infections among schoolchildren across Osh oblast, Kyrgyzstan. The diagnostic approach consisted of duplicate Kato-Katz thick smears from a single stool sample and an adhesive tape test. A questionnaire was administered to identify risk factors for infections. A total of 1262 schoolchildren aged 6–15 years were recruited; 41% of them harboured at least one of the eight identified helminth species. The two most prevalent helminths were Ascaris lumbricoides (23.1%) and Enterobius vermicularis (19.3%). Lower prevalences were found for Hymenolepis nana (4.4%), Fasciola hepatica (1.9%) and Dicrocoelium dendriticum (1.8%). Washing raw vegetables was a protective factor with regard to A. lumbricoides infection (odds ratio (OR) = 0.69, p = 0.022); tap water was borderline protective (OR = 0.56, p = 0.057). Children of the richest families were at a lower risk of E. vermicularis infection than the poorest ones (OR = 0.41, p = 0.011). Sharing the bed with more than one person was a risk factor for E. vermicularis infection (OR = 2.0, p = 0.002). The results call for targeted interventions against intestinal helminths in Osh oblast. In a first stage, annual deworming of schoolchildren and other high-risk groups with albendazole or mebendazole should be implemented, and reliable diagnosis and additional anthelminthic drugs should be made available. Subsequently, transmission control including locally-adapted health education, improved water supply and adequate sanitation should become the central features.

Bayes-LQAS: classifying the prevalence of global acute malnutrition

Lot Quality Assurance Sampling (LQAS) applications in health have generally relied on frequentist interpretations for statistical validity. Yet health professionals often seek statements about the probability distribution of unknown parameters to answer questions of interest. The frequentist paradigm does not pretend to yield such information, although a Bayesian formulation might. This is the source of an error made in a recent paper published in this journal. Many applications lend themselves to a Bayesian treatment, and would benefit from such considerations in their design. We discuss Bayes-LQAS (B-LQAS), which allows for incorporation of prior information into the LQAS classification procedure, and thus shows how to correct the aforementioned error. Further, we pay special attention to the formulation of Bayes Operating Characteristic Curves and the use of prior information to improve survey designs. As a motivating example, we discuss the classification of Global Acute Malnutrition prevalence and draw parallels between the Bayes and classical classifications schemes. We also illustrate the impact of informative and non-informative priors on the survey design. Results indicate that using a Bayesian approach allows the incorporation of expert information and/or historical data and is thus potentially a valuable tool for making accurate and precise classifications.

Knowledge and coverage of Prevention of Mother to Child Transmission (PMTCT) in Eritrea

Objective: To explore the level of knowledge on prevention of mother to child transmission of HIV in both men 15-54 years and women 15-49 years of age. Methods: A community-based survey was conducted in October-November 2005 in 45 sub zones of Eritrea. Data were collected using the Lot Quality Assurance Sampling (LQAS) method. Results: Although 81.8% of men 15-54 and 75.5% of women 15-49 years of age know that HIV can be transmitted from mother to the child, only 33.7 % of men and 26% of women know that the risk of transmission can be reduced. The result varies across zones and various socio-demographic characteristics. Conclusion: Although there is high awareness on the risk of HIV transmission from the mother to the child, the knowledge that the risk can be reduced is very low and extensive education for both men and women is recommended

Clustered lot quality assurance sampling to assess immunisation coverage: increasing rapidity and maintaining precision

Vaccination programmes targeting disease elimination aim to achieve very high coverage levels (e.g. 95%). We calculated the precision of different clustered lot quality assurance sampling (LQAS) designs in computer-simulated surveys to provide local health officers in the field with preset LQAS plans to simply and rapidly assess programmes with high coverage targets. We calculated sample size (N), decision value (d) and misclassification errors (alpha and beta) of several LQAS plans by running 10 000 simulations. We kept the upper coverage threshold (UT) at 90% or 95% and decreased the lower threshold (LT) progressively by 5%. We measured the proportion of simulations with < or =d individuals unvaccinated or lower if the coverage was set at the UT (pUT) to calculate beta (1-pUT) and the proportion of simulations with >d unvaccinated individuals if the coverage was LT% (pLT) to calculate alpha (1-pLT). We divided N in clusters (between 5 and 10) and recalculated the errors hypothesising that the coverage would vary in the clusters according to a binomial distribution with preset standard deviations of 0.05 and 0.1 from the mean lot coverage. We selected the plans fulfilling these criteria: alpha < or = 5% beta < or = 20% in the unclustered design; alpha < or = 10% beta < or = 25% when the lots were divided in five clusters. When the interval between UT and LT was larger than 10% (e.g. 15%), we were able to select precise LQAS plans dividing the lot in five clusters with N = 50 (5 x 10) and d = 4 to evaluate programmes with 95% coverage target and d = 7 to evaluate programmes with 90% target. These plans will considerably increase the feasibility and the rapidity of conducting the LQAS in the field.

An assessment of Lot Quality Assurance Sampling to evaluate malaria outcome indicators: extending malaria indicator surveys.

Large investments and increased global prioritization of malaria prevention and treatment have resulted in greater emphasis on programme monitoring and evaluation (M&E) in many countries. Many countries currently use large multistage cluster sample surveys to monitor malaria outcome indicators on a regional and national level. However, these surveys often mask local-level variability important to programme management. Lot Quality Assurance Sampling (LQAS) has played a valuable role for local-level programme M&E. If incorporated into these larger surveys, it would provide a comprehensive M&E plan at little, if any, extra cost. The Mozambique Ministry of Health conducted a Malaria Indicator Survey (MIS) in June and July 2007. We applied LQAS classification rules to the 345 sampled enumeration areas to demonstrate identifying high- and low-performing areas with respect to two malaria program indicators-'household possession of any bednet' and 'household possession of any insecticide-treated bednet (ITN)'. As shown by the MIS, no province in Mozambique achieved the 70% coverage target for household possession of bednets or ITNs. By applying LQAS classification rules to the data, we identify 266 of the 345 enumeration areas as having bednet coverage severely below the 70% target. An additional 73 were identified with low ITN coverage. This article demonstrates the feasibility of integrating LQAS into multistage cluster sampling surveys and using these results to support a comprehensive national, regional and local programme M&E system. Furthermore, in the recommendations we outlined how to integrate the Large Country-LQAS design into macro-surveys while still obtaining results available through current sampling practices.