Combined multiplex panel test results are a poor estimate of disease prevalence without adjustment for test error.

Multiplex panel tests identify many individual pathogens at once, using a set of component tests. In some panels the number of components can be large. If the panel is detecting causative pathogens for a single syndrome or disease then we might estimate the burden of that disease by combining the results of the panel, for example determining the prevalence of pneumococcal pneumonia as caused by many individual pneumococcal serotypes. When we are dealing with multiplex test panels with many components, test error in the individual components of a panel, even when present at very low levels, can cause significant overall error. Uncertainty in the sensitivity and specificity of the individual tests, and statistical fluctuations in the numbers of false positives and false negatives, will cause large uncertainty in the combined estimates of disease prevalence. In many cases this can be a source of significant bias. In this paper we develop a mathematical framework to characterise this issue, we determine expressions for the sensitivity and specificity of panel tests. In this we identify a counter-intuitive relationship between panel test sensitivity and disease prevalence that means panel tests become more sensitive as prevalence increases. We present novel statistical methods that adjust for bias and quantify uncertainty in prevalence estimates from panel tests, and use simulations to test these methods. As multiplex testing becomes more commonly used for screening in routine clinical practice, accumulation of test error due to the combination of large numbers of test results needs to be identified and corrected for.

Trends in deprivation in hospitalisations of Indigenous children and young people in Aotearoa New Zealand.

AIM: To examine the 20-year trends in socio-economic inequities in hospitalisations of Maori and non-Maori non-Pacific (NMNP) under-25-year olds in Aotearoa New Zealand. METHODS: Hospital discharge data for Maori and NMNP taitamariki aged under-25 years were extracted from the National Minimum Dataset for the period 2000-2019. Acute or arranged admissions to hospital were included where the primary diagnosis was for a medical condition. Age- and gender-standardised rates (per 1000, 0-24-year old) were calculated for both ethnic groups by area deprivation using the 2013 NZ census estimated resident population. For each ethnic group, inequity indices of socio-economic deprivation (Slope Index of Inequality and Relative Index of Inequality) were computed, using regression modelling, to quantify inequity of medical condition-related hospitalisations and its changes over time. RESULTS: Hospitalisation rates for medical conditions were consistently higher for Maori than for NMNP under-25-year olds from 2000 to 2019. Maori taitamariki residing in the most deprived (quintile 5) areas were more likely than NMNP to be hospitalised for a medical condition at each time point. Deprivation inequities existed for both ethnic groups and were greater for Maori. Despite reducing deprivation inequities over time, ethnic differences persist on both absolute and relative scales. CONCLUSION: Deprivation inequities in hospitalisation for medical conditions persist for Maori taitamariki compared with NMNP and highlights society's tolerance of enduring inequity in health outcomes.

Shoulder dystocia, umbilical cord blood gases and neonatal encephalopathy.

The interpretation of umbilical cord gases may not be straightforward following shoulder dystocia. We reviewed Perinatal and Maternal Mortality Review Committee data from New Zealand infants with moderate and severe neonatal encephalopathy (NE) for 2010-2017 inclusive. If one or more of: pH of ≤7.1; base excess of ≤-12 mmol/L; or lactate of ≥6 mmol/L were present it was considered an abnormal result. One-third (12/36) of infants born following shoulder dystocia had documented umbilical cord gases within the normal range. It is important for clinicians to be aware of this possibility when assessing newborn infants with NE.