Simultaneous co-detection of wild-type and vaccine strain measles virus using the BD MAX system

Is it or is it not? Lessons learned from a case of suspected vaccine strain measles

OBJECTIVE

Measles continues to be a threat to Australia. While post-eradication risks are low, imported measles cases from overseas travellers who are non-immune can cause small outbreaks. This case report discusses the challenge of identifying wild-type measles in an individual who was recently vaccinated with measles-containing vaccine (MCV).

METHODS

A positive polymerase chain reaction (PCR) result for measles for an adult who had recently received a measles-containing vaccine was notified. Investigation revealed no known epidemiological link, recent overseas travel or contact with recent measles cases during the incubation period.

RESULTS

The results of the initial sequencing to distinguish between wild-type and vaccine-strain measles were inconclusive. A decision was made to re-run the genotyping, collect additional specimens and quarantine the case until a definitive result was obtained. Sequencing and genotyping revealed that this indeed was a wild-type measles strain.

CONCLUSIONS

Changing epidemiology of measles means distinguishing between wild-type and vaccine-strain measles has become a new challenge. Implications for public health: The reflection of the public health management of this case has provided a valuable teaching tool for public health professionals globally, particularly in low incidence measles countries.

Analysis of Clinical Isolates of Extended-Spectrum β-Lactamase-Producing Bacteria with Primer and Probe Sets Developed to Detect blaCTX-M, blaTEM, and blaSHV Using a Fully Automated Gene Detection System

In this study, we evaluated extended-spectrum β-lactamase (ESBL)-producing bacteria with the newly developed primer and probe sets to detect bla_CTX-M, bla_TEM, and bla_SHV using BD MAX^TM, a fully automated multiplex polymerase chain reaction assay system. In 36 isolates confirmed by whole-genome sequencing to have bla_CTX-M, bla_TEM, or bla_SHV, the developed primer and probe sets accurately detected each gene without being influenced by the presence of other β-lactamase genes. In nine control strains that do not harbor either bla_CTX-M, bla_TEM, or bla_SHV no cross-reaction was observed. In 191 strains phenotypically determined to be ESBL-producers by conventional antimicrobial susceptibility tests, 189 strains were blaC_TX-M-, bla_TEM-, or bla_SHV-positive as assessed by BD MAX^TM using the developed primer and probe sets, and two strains were negative for these genes. Whole-genome sequencing revealed that these two strains were phenotypically false-positive ESBL-producers. The accuracy of the primer and probe sets seems to be satisfactory, and they may be applicable to detect CTX-M-type ESBL-producing bacteria.

Simultaneous Detection and Differentiation between Wild-Type and Vaccine Measles Viruses by a Multiplex Real-Time Reverse Transcription-PCR Assay

Measles is one of the most contagious viral respiratory infections and was declared to be eliminated from Canada in 1998; however, measles cases and outbreaks still occur every year through reintroduction from other parts of the world. Laboratory confirmation of measles virus (MV) RNA by real-time PCR provides a definitive diagnosis, and molecular analysis to determine the genotype is the only way to distinguish between wild-type and vaccine strains. This distinction is important since live attenuated vaccine strains are able to replicate in the patient and can be associated with rash and fever but are poorly transmissible, if at all. Prompt reporting of measles cases to local authorities, including differentiation between wild-type and vaccine strains, allows for optimal management and contact tracing. The development and validation of a multiplex real-time reverse transcription-PCR (rtRT-PCR) assay for the simultaneous detection and differentiation of the Moraten and Schwarz vaccine strains from presumptive wild-type MV in a format that can be easily implemented for high-throughput testing of patient samples are reported here. This assay is sensitive, specific, reproducible, and 100% accurate in comparison with the gold standard comparator assay.