Top 5 Infectious Disease News Stories Week of December 28-January 3

Emerging Resistance in Pseudomonas Treatment: Key Insights from the CACTUS Study

The CACTUS Study compared the effectiveness of ceftolozane-tazobactam (CT) and ceftazidime-avibactam (CZA) in treating multidrug-resistant (MDR) Pseudomonas aeruginosa infections, finding similar clinical success rates (62% for CT and 55% for CZA) and comparable 30-day mortality rates (20% for CT and 19% for CZA). Although, both treatments saw resistance development in 1 in 5 patients, which is largely attributed to Pseudomonas' ability to upregulate chromosomal resistance mechanisms. In an interview with Jason M Pogue, PharmD, he explained that this form of resistance is a long-standing challenge with Pseudomonas, and it is not surprising to see it develop even with newer beta-lactam agents. He emphasized the importance of strategies such as dose optimization, combination therapy, and continued drug development to manage resistance and improve treatment outcomes for Pseudomonas infections.

The First CDC Morbidity and Mortality Weekly Report (MMWR) of 2025

The CDC's 2023 Morbidity and Mortality Weekly Report highlights two significant public health concerns in the US: the largest recorded outbreak of blastomycosis, linked to a paper mill in Michigan, and a 56% increase in tularemia cases from 2011 to 2022. The Michigan outbreak involved 162 confirmed cases of blastomycosis, a fungal infection, among mill workers, marking the largest such outbreak in US history. Despite challenges in identifying the source and environmental samples, coordinated public health actions quickly addressed the issue. Meanwhile, tularemia cases rose across 47 states, particularly affecting children, older adults, and American Indian/Alaska Native populations. The increase in tularemia may reflect a true rise in infections and improved diagnostic practices. These cases underline the need for enhanced prevention, surveillance, and timely responses to protect vulnerable groups and mitigate further outbreaks.

RSV Vaccine for Immunocompromised Seniors Shows Limited Seroconversion

A study examining the effectiveness of two FDA-approved RSV vaccines in immunocompromised seniors found limited seroconversion, with 40% of participants not achieving detectable antibody levels. The study focused on organ transplant recipients and others with immune system disorders who received either GSK's adjuvanted RSVA-AS01 (Arexvy) or Pfizer's nonadjuvanted RSVpreF (Abrysvo). While the vaccines showed strong antibody responses in healthy seniors, immunocompromised individuals developed fewer antibodies. Notably, those receiving the adjuvanted Arexvy vaccine had higher levels of neutralizing antibodies. Researchers suggest that additional vaccine doses may be necessary to enhance the immune response in this population and emphasize the need for further studies on adjuvant-enhanced vaccines to improve efficacy in immunocompromised patients.

Clinician Feedback Reports on Antibiotics Shape Usage in Pediatric Inpatients With Pneumonia

A study from the Children’s Hospital of Philadelphia (CHOP) focused on improving antibiotic stewardship for pediatric community-acquired pneumonia (CAP) inpatients through clinician feedback reports. The intervention, which included monthly reports and group-level performance discussions, led to an 18% increase in adherence to appropriate antibiotic choices and durations. Pre-intervention, 52% of encounters adhered to the recommended guidelines, which rose to 80% post-intervention. Despite no changes in hospital revisit rates or length of stay, the study found that shorter antibiotic durations did not impact recovery outcomes, reducing the risk of side effects for children. The study highlights the effectiveness of using electronic health record data for feedback-based stewardship, making it a feasible approach for improving antibiotic use in hospital settings.

CDC: Genetic Mutations of Avian Influenza Emerge in First Severe US Case

The CDC reports a severe case of avian influenza A(H5N1) in a patient from Louisiana, marking the first such case in the US with severe symptoms requiring hospitalization. The virus in this patient has mutations not seen in previous cases, suggesting they emerged as the virus replicated within the patient. The patient was infected with the D11 genotype of A(H5N1), which is related to strains found in wild birds and poultry in the US and Canada, but differs from the B313 genotype causing other outbreaks. Genetic analysis revealed some rare changes in the virus, particularly in the hemagglutinin gene, but no mutations associated with reduced antiviral susceptibility. While the mutations appeared specific to the human host environment, there has been no evidence of human-to-human transmission. The patient, who had a history of exposure to backyard poultry, remains the only severe case in the US, with previous infections showing only mild symptoms.