In its weekly flu season update today, the US Centers for Disease Control and Prevention (CDC) said though activity remains low nationally, there are slight increases in children, along with the first confirmed pediatric flu death of the 2024-25 season.

A few markers showed small increases last week, including percent positivity, which remains below the national baseline. Emergency department visits for flu increased a bit in pediatric age-groups.

Of two child flu deaths reported to the CDC this week, one was reported from February and was added to the previous season's pediatric deaths, which are now at 204. The other occurred in the middle of October and was related to an unsubtyped influenza A virus.

In updates on other respiratory viruses, today the CDC said COVID-19 activity is stable and declining in most areas. Wastewater SARS-CoV-2 levels remain low and are highest in the Midwest. Tracking by WastewaterSCAN, a national wastewater monitoring system based at Stanford University in partnership with Emory University, shows virus detections in the low category, with a downward trend over the past 3 weeks.

Shifting COVID variant proportions, rising RSV activity

In a SARS-COV-2 variant update today, the CDC reported the first decline in KP.3.1.1 proportions, which dropped from 57% to 52% over the past 2 weeks. Meanwhile, the proportion of XEC, a recombinant of two JN.1 viruses, continued a steady rise, up from 17% to 28% over the same period. 

Another variant, called MC.1, also showed increasing proportions. In an update last week from the CDC's National Center for Immunization and Respiratory Diseases, the group said MC.1 is a descendant of KP.3.1.1 and that the updated vaccine is expected to work well against new variants that may become dominant, including XEC and MC.1.

Regarding respiratory syncytial virus (RSV), the CDC said it is seeing signs of rising activity in the southern, southeastern, and middle Atlantic regions, especially in young children.

Pertussis (whooping cough) cases in the United States this year have risen fivefold compared to the same time last year, as disease activity returned to a prepandemic pattern, the US Centers for Disease Control and Prevention (CDC) said yesterday. So far this year, cases are tracking higher than 2019, the year before the COVID-19 pandemic.

Some state health departments have warned of rising cases, including Washington, which said yesterday that, as of November 2, nearly 1,200 cases have been reported statewide, up sharply from 51 cases reported during the same period in 2023. 

It said it expects a further rise in cases in both unvaccinated and vaccinated people given waning immunity from the acellular vaccine. 

Tao Sheng Kwan-Gett, MD, a pediatrician and chief health officer at the Washington State Department of Health, said the surge in cases is a reminder of the critical role of vaccines for protecting vulnerable people, especially infants younger than 1 year old. "To protect babies from whooping cough, people of all ages should get up to date on pertussis vaccination, and anyone with symptoms should see a health care provider to see if testing and antibiotic treatment are needed."

Multiple factors likely contribute to rise

The CDC said several factors are probably contributing to a post-pandemic rise in pertussis activity. Aside from waning vaccine immunity, they include improved recognition by healthcare providers, greater access to and use of diagnostics, and increased surveillance and reporting to health departments.

Caused by Bordetella pertussis, the disease is highly contagious and can begin with common cold symptoms including runny nose, but can lead to severe coughing that can last weeks to months. Infants are at highest risk for severe illness and death. In Washington, 28 pertussis patients were hospitalized, including 12 babies. 

Disease surveillance and genomic analyses in northeast China identifies the emerging tick-borne Yezo virus in 2% of 988 participants, prompting researchers to urge clinicians to be vigilant in patients with symptoms of infection.

For the study, published in The Lancet Infectious Diseases, researchers from Shandong University conducted Yezo virus surveillance at a hospital in Heilongjiang Province.

The team collected sera from patients who sought care for a tick bite from May to July in 2022, 2023, and 2024 to conduct genomic sequencing, real-time-polymerase chain reaction, and indirect immunofluorescence assay. They used cell culture to isolate the virus.

"Yezo virus (YEZV) is an emerging tick-borne pathogen, which was initially reported in Japan in 2021," the authors noted. "Only one patient had been reported in China so far." 

Differentiating Yezo signs, symptoms

Eighteen participants had Yezo virus infections (12 male, 6 female; median age, 53 years), and 8 were hospitalized. Symptoms included fever (100%), headache (56%), dizziness (50%), malaise (17%), low back pain (17%), cough (17%), gastrointestinal problems (50%), and neurologic issues (28%). Signs included rash (50%), abnormal lymph nodes (22%), and, among 16 patients, low levels of lymphocytes (63%) and platelets (31%).

YEZV should be differentiated from those with other tick-borne pathogens, which can cause similar clinical manifestations.

High liver transaminase levels were observed in 72% of participants, while elevated concentrations of the enzymes lactate dehydrogenase or α-hydroxybutyric dehydrogenase were seen in 50%, serum amyloid protein A in 72%, and C-reactive protein in 56%.

Eight (7%) of 119 Ixodes persulcatus ticks—or taiga ticks—removed from patients tested positive for Yezo, and three strains were isolated from sera. Phylogenetic analyses showed that Yezo viruses in patients or ticks belonged to two clades with distinct mutations.

"YEZV should be differentiated from those with other tick-borne pathogens, which can cause similar clinical manifestations," the researchers wrote.

In a related commentary, Keita Matsuno, DVM, of Hokkaido University, called for expanded surveillance: "Further studies are needed to identify currently unrecognised endemic areas of Yezo virus infections, especially in northern Europe and northern Asia, where I persulcatus ticks are widely distributed."

• Seven countries reported new polio cases the week, including Pakistan, with four new infections involving wild poliovirus type 1 (WPV1), according to the latest weekly update from the Global Polio Eradication Initiative. Pakistan and Afghanistan are the two remaining countries where WPV1 is still endemic, and both have reported steep rises this year. Pakistan's new cases—one in Balochistan and three in Khyber Pakhtunkhwa—push the country's total for the year to 45 cases. In Africa, five countries reported more vaccine-derived poliovirus cases, including Senegal, with its first circulating vaccine-derived poliovirus type 2 (cVDPV2) case for the year. The other four are the Democratic Republic of the Congo, Ethiopia, Niger, and Nigeria. In the Middle East, Yemen reported two cVDPV2 cases in Aden in patients with paralysis onset in September.
• Law enforcement officials in South Carolina's Beaufort County have alerted residents about an escape of 43 rhesus macaque monkeys from an Alpha Genesis research facility, CBS News reported. The company provides the animals to research labs, conducts research, and oversees a colony of free-range monkeys on South Carolina's Morgan Island. The Centers for Disease Control and Prevention said the public health risk is low as long as people don't approach or come in contact with the monkeys. Authorities said the escapees are very young females that hadn't yet been used for research. In a Facebook update today, the Yemassee Police Department said the primates haven't been recaptured yet and are playfully exploring the company's perimeter fence as the company keeps close watch of the situation.
• In Colorado, Boulder County reported its first human tularemia case since 2015, which involves a person who lives near Boulder who has the rare pneumonic form of the disease. In a November 1 statement, the county said the patient's symptoms began on October 2 with fever, which worsened to include altered mental status and fluid on the lungs. An investigation found that the patient had exposure to a cat and a dog, though the animals have shown no illness signs. Health officials said they aren't ruling out an insect bite as the infection source. Tularemia is caused by the bacterium Francisella tularensis, and wild animals such as rodents and rabbits are known to carry the pathogen, which is highly infectious and is classified as a high-priority bioterrorism agent by the US government.