Performance Characteristics of Six Immunoglobulin M Enzyme-Linked Immunosorbent Assays Used for Laboratory Confirmation of Measles.

Laboratory confirmation of infection is an essential component of measles surveillance. Detection of measles-specific IgM in serum by enzyme-linked immunosorbent assay (ELISA) is the most common method used to confirm measles infection. ELISA formats vary, as does the sensitivity and specificity of each assay. Specimens collected within 3 days of rash onset can yield a false-negative result, which can delay confirmation of measles cases. Interfering substances can yield a false-positive result, leading to unnecessary public health interventions. The IgM capture assay developed at the Centers for Disease Control (CDC) was compared against five commercially available ELISA kits for the ability to detect measles virus-specific IgM in a panel of 90 well-characterized specimens. Serum samples were tested in triplicate using each commercial kit as recommended by the manufacturer. Using the CDC measles IgM capture assay as the reference test; the sensitivity and specificity for each commercial kit ranged from 50 to 83% and 86.9 to 98%, respectively. Discrepant results were observed for samples tested with all five commercial kits and ranged from 13.8 to 28.8% of the specimens tested. False-positive results occurred in 2.0 to 13.1% of sera, while negative results were observed in 16.7 to 50% of sera that were positive by the CDC measles IgM capture assay. Evaluation and interpretation of measles IgM serologic results can be complex, particularly in measles elimination settings. The performance characteristics of a measles IgM assay should be carefully considered when selecting an assay to achieve high-quality measles surveillance.

Measles infection in persons with secondary vaccine failure, New York City, 2018-19.

A large measles outbreak in New York City, which included cases among vaccinated persons and adults presumed to be immune, provided the opportunity to better understand vaccine failure and the potential impact on measles transmission. Immunoglobulin G (IgG) avidity can distinguish primary (low avidity IgG, indicating no evidence of prior immunity) versus secondary vaccine failure (high avidity IgG, indicating prior immune response and waning antibody). Measles IgG avidity was measured on samples from 62 persons: avidity was high in 53 (16 vaccinated and 37 with unknown vaccination history) and low in 9 (1 recently vaccinated and 8 with unknown vaccination history). Secondary transmission from 2 persons with high-avidity IgG results occurred. These findings illustrate that in settings of sustained measles elimination, measles infection and transmission can occur in persons with secondary vaccine failure, underscoring the need to maintain a high index of suspicion for measles during an outbreak despite prior or presumed prior vaccination.

Qualitative Variation among Commercial Immunoassays for Detection of Measles-Specific IgG.

Measurement of measles virus-specific IgG is used to assess presumptive evidence of immunity among immunocompetent individuals with uncertain immune or vaccination status. False-negative test results may lead to unnecessary quarantine and exclusion from activities such as employment, education, and travel or result in unnecessary revaccination. In contrast, false-positive results may fail to identify susceptible individuals and promote spread of disease by those who are exposed and unprotected. To better understand the performance characteristics of tests to detect measles IgG, we compared five widely used, commercially available measles IgG test platforms using a set of 223 well-characterized serum samples. Measles virus neutralizing antibodies were also measured by in vitro plaque reduction neutralization, the gold standard method, and compared to IgG test results. Discrepant results were observed for samples in the low-positive ranges of the most sensitive tests, but there was good agreement across platforms for IgG-negative sera and for samples with intermediate to high levels of IgG. False-negative test results occurred in approximately 11% of sera, which had low levels of neutralizing antibody.

Ward nurses' evaluation of critical care outreach.

Following the recommendation to introduce critical care outreach, two different models on two hospital sites were introduced within a large teaching Trust. To establish ward nurses' views and opinions of important components of the two outreach models, a questionnaire survey was undertaken involving 134 ward nurses on the awareness of outreach, accessibility of outreach and usage of outreach. The results identified a high level of user satisfaction amongst ward nurses. Awareness of critical care outreach and how to access the service within a hospital site was good, with little differences between the two different models. Outreach was found to provide ward nurses with better skills, more knowledge, advice and support. Providing a 24-h service and continual critical care education and training opportunities are the suggested ways to improve outreach in the future.