Recent MMR vaccination may lead to false-positive measles test results

News brief
measles rash
Photo of vaccine-derived measles rash courtesy of CDC 

Children who are given polymerase chain reaction (PCR) tests that simultaneously look for multiple causes of a rash may test falsely positive for measles if they recently had a dose of the measles, mumps, rubella (MMR) vaccine, according to a new study in Morbidity and Mortality Weekly Report.

MMR vaccine includes live attenuated measles virus, which is detectable by PCR tests but does not cause active infections in people with healthy immune systems. From September 2022 to January 2023, however, the Tennessee Department of Health received two reports of measles detected by PCR panels conducted for rashes.

The children (aged 1 and 6 years) had no known risk factors for measles, but their rashes appeared 11 to 13 days after routine MMR vaccination. Further testing showed the PCR test had detected live attenuated measles virus used in MMR vaccine.

1% of tests positive for measles

The Tennessee cases triggered a wider nationwide assessment of PCR panels. From May 2022 to April 2023, among 1,548 syndromic PCR panels conducted for rashes, 17 (1.1%) returned positive test results for measles virus.

In 14 of the 17 positive tests, patients had received MMR vaccine an average 12 days before specimen collection, and none had known risk factors for acquiring measles, the authors said.

Inclusion of measles virus in syndromic PCR panels can result in incidental detection of measles vaccine virus.

"As demonstrated by this analysis, inclusion of measles virus in syndromic PCR panels can result in incidental detection of measles vaccine virus," the authors said. "When measles infection is not clinically suspected but detected by syndromic PCR testing, public health agencies should consider the likelihood of incidental measles vaccine virus detection by assessing measles vaccination history and risk factors."

US flu, COVID-19, RSV levels all decline

News brief

Flu indicators dropped last week for the second consecutive week, as markers for COVID and respiratory syncytial virus (RSV) also continued their downward trends, the US Centers for Disease Control and Prevention (CDC) said today in its latest data updates.

Flu levels drop, but still above baseline

Over the past few months, flu activity showed a post-holiday rise that mainly varied by region and was partly fueled by increased circulation of influenza B, which typically occurs later in the flu season. In its weekly FluView update today, the CDC said test positivity for both influenza A and influenza B decreased last week compared to the previous week. Influenza A is still dominant, making up 59.3% of positive results at public health labs, with influenza B at 40.7%

negative covid test
Cory Doctorow / Flickr cc

Other markers declined, including the percentage of outpatient visits for flulike illness, which is still above the national baseline, and hospitalizations. Deaths overall remained steady, and the CDC reported 5 more pediatric flu deaths, raising the season's total to 126, compared with 184 for the entire 2022-23 season.

Steady decline in COVID indicators

In COVID data updates, the CDC reported more steady declines in virus impacts, both the severity markers and the early indicators. Wastewater detections of SARS-CoV-2, considered an early indicator, remained at the low level, with declines continuing in all regions of the country.

Also today, the CDC released its latest variant proportion update, which shows that JN.1 is still dominant but that levels of one of its offshoots, JN.1.13, continue to rise and are now at about 11%.

Pennsylvania reports H1N2v flu case

News brief

The Pennsylvania Department of Health has reported a variant H1N2 (H1N2v) infection in a patient younger than 18 years, marking the nation's first variant influenza A case of 2024, the Centers for Disease Control and Prevention (CDC) said today in its weekly influenza update.

three little pigs
liz west / Flickr cc

The patient sought care in early March, was hospitalized, and has since recovered.

An investigation into the source of the illness found that the patient had contact with pigs before symptoms began. Mild illness was reported in two of the patient's close contacts, who also had contact with pigs. They were sick before the patient became ill. No person-to-person spread of H1N2v has been identified.

The CDC reported four variant flu infections over the 2022-2023 flu season, of which two involved H1N2v.

Study documents mortality, costs of pneumococcal disease, pneumonia

News brief
Doctor with chest x-ray
DragonImages / iStock

Data from US hospitals highlight the clinical and economic burden of invasive pneumococcal disease (IPD) and non-invasive all-cause pneumonia (ACP), researchers reported yesterday in the International Journal of Infectious Diseases.

Using data collected from 90 large and small US hospitals in urban and rural areas from October 2015 through February 2020, researchers from Merck and from Becton, Dickinson and Company analyzed data on hospitalized adults with an ICD-10 code for IPD, non-invasive ACP, or a positive Streptococcus pneumoniae culture or antigen test. The primary outcomes of interest included in-hospital mortality, length of stay (LOS), costs per admission, and hospital margin per admission. The researchers also analyzed antimicrobial susceptibility data.

Of the 88,182 adult patients (50.7% female) included in the study, 98.6% had non-invasive ACP and 40.2% were younger than 65 years. Of 1,450 culture-positive patients, 37.7% had an isolate that was resistant to one or more antibiotic class.  The overall observed hospital mortality rate was 8.3%, median LOS was 6 days, median cost per admission was $9,791, and median hospital margin per admission was $11. Patients with IPD had similar mortality rates and hospital margins compared with non-invasive ACP, but greater LOS and costs per admission.

Age, ICU admission linked to mortality risk

Although older age was associated with higher mortality rates, similar median LOS and costs per admission were observed across all age-groups. In adjusted analyses, the variables with the most impact on in-hospital mortality were intensive care unit admission (odds ratio [OR], 7.19; 95% confidence interval [CI], 6.81 to 7.59) and being older than 75 (OR, 4.27; 95% CI, 3.81 to 4.78). Other significant variables included being older than 50, prior 90-day admission, high or moderate risk for pneumococcal disease, and Medicare or "other" insurance.

"Our study demonstrates that adults with IPD and non-invasive ACP are at risk for poor health outcomes," the study authors wrote. "A combined approach to reducing disease incidence, including expanded vaccination programs, improved diagnostics, new anti-pneumococcal antibiotics, and targeted stewardship programs, may be needed to reduce the burden of this disease."

Higher rates of hospitalization, deaths among MS patients with COVID-19

News brief

New real-world data being presented at this year's European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) conference shows that people living with multiple sclerosis (MS) face a much higher risk of being hospitalized and dying from COVID-19 than the general population, in part due to B-cell depletion therapies that can cause poor responses to vaccination.

The findings are based on nearly 12 million people aged 12 years and older in England analyzed as part of the INFORM study, which looked at outcomes among immunocompromised people compared with the general population during the Omicron wave. Among the 12 million were 16,350 (0.1%) people with MS, 12,905 of whom (78.9%) had been fully vaccinated with at least three doses of a COVID-19 vaccine by January 1, 2022.

In the MS group there were 215 COVID-19 hospitalizations and 25 COVID-19 deaths, resulting in incidence rates of 1.28 and 0.14 per 100 person-years, respectively. In the general population, the rates of hospitalization and death was 0.24 and 0.06 per 100 person-years, respectively.

Quadruple the risk of death

"Having multiple sclerosis in itself doesn't increase the risk of getting COVID-19, rather it's the taking of immune modifying medicine such as B-cell depletion therapies that can reduce the effectiveness of vaccines by preventing the immune system from mounting a robust protective response," said lead author Jennifer Quint, PhD, from Imperial College London in an ECCMID press release.

It's the taking of immune modifying medicine such as B-cell depletion therapies that can reduce the effectiveness of vaccines

In analyses that adjusted for age and sex, MS was associated with a seven-times-greater risk of COVID-19 hospitalization and fourfold increased risk of dying from COVID-19 compared to the general population, the authors said.

"With new variants constantly emerging, people living with MS should be considered an important high-risk group for COVID-19 hospitalisation and death for which additional preventive measures and multi-layered public health protections are urgently needed," Quint said.

This week's top reads