US flu activity is low and declining further, according to the latest FluView update today from the Centers for Disease Control and Prevention (CDC).

The percentage of outpatient visits for influenza-like illness (ILI), or respiratory illness, dropped slightly from 2.1% the previous week to 1.9% last week (see CDC graph at left). The number of patients hospitalized for flu dropped from 2,336 to 2,008. As with the previous week, no state reported moderate, high, or very high ILI activity.

Test positivity for flu is down to 2.9%, from 3.6% the previous week. Hospitalizations and deaths are both down.

The CDC confirmed only 1 new flu-related pediatric death today, raising the number for the 2024-25 season to 227. The death occurred in January and was caused by the H1N1 strain. The 227 US pediatric deaths are the most since 2009-10, when the CDC reported 288 pediatric deaths.

COVID-19, RSV activity also low

Meanwhile, COVID-19 levels remain low, according to CDC data updates today. Wastewater detections last week remained generally low, but Louisiana recorded high levels. The percentage of overall deaths caused by COVID last week stayed steady, at 0.6%, compared with 0.2% for flu.

In its update on the three leading respiratory illnesses—flu, COVID-19, and respiratory syncytial virus (RSV)—the CDC notes that, nationally, flu (2.9%), COVID (2.9%), and RSV (0.9%) test positivity stayed about the same. Wastewater levels for COVID are low, while for influenza A and RSV they are very low.

From the end of December 2024 to April 26 of this year, five countries in the Americas confirmed 212 yellow fever cases and 85 related deaths, for a case-fatality rate of 40%, the World Health Organization (WHO) said in any update today.

Those numbers represent a more than tripling of cases of the mosquito-borne disease recorded for all of 2024, the agency said.

Most cases, deaths in Brazil

The 212 cases were confirmed from December 29, 2024, through April 26, 2025, with data for Ecuador analyzed through May 2. Brazil has the most cases and deaths—110 and 44, respectively. Colombia has 60 cases and 24 deaths, Peru 35 cases and 12 deaths, Ecuador 4 fatal cases, and Bolivia, 3 infections, including 1 fatal case.

"In 2024, human cases of yellow fever were reported mainly across the Amazon region of Bolivia, Brazil, Colombia, Guyana, and Peru," the WHO said. "In 2025, however, cases have been detected mainly in areas outside the Amazon region, including in the state of São Paulo, Brazil and the Tolima department, Colombia." Last year, the Americas region had 61 confirmed yellow fever illnesses.

The five affected countries have implemented actions to respond to the outbreaks, focusing on strengthening preventive measures, improving surveillance, and implementing immunization campaigns. 

The WHO determined that the risk of yellow fever spread in the region is high. "The occurrence of yellow fever cases outside of the Amazon basin, combined with high fatality, varying vaccination coverage across affected countries, and limited vaccine supply, contributes to the overall classification of yellow fever risk in the Region of the Americas, especially in endemic countries, as high," the agency said. 

"WHO emphasizes the importance of active surveillance, timely laboratory testing, cross-border coordination, and information sharing. Vaccination remains the primary means for the prevention and control of yellow fever."

Ebola patients in the Democratic Republic of the Congo (DRC) were much less likely to die if they were vaccinated against the viral hemorrhagic infection and received prompt treatment with monoclonal antibodies or an antiviral drug and enhanced supportive care, according to a secondary analysis published yesterday in Virology Journal.

Investigators from the University of Kinshasa in the DRC and the University of Technology in Sydney, Australia, examined the medical data of 781 hospitalized patients at one of four Ebola treatment centers in the North Kivu region. The aim was to gauge 28-day death rates and identify predictors of survival during the country's 10th Ebola outbreak (August 2018 to February 2020). 

Vaccinated patients 1.7 times less likely to die

In total, 20% of patients were vaccinated against Ebola at study inclusion. Intervention patients received a monoclonal antibody treatment (mAB; REGN-EB3 [31%], MAb114 [27%], or ZMapp [13%]), or the antiviral remdesivir (21%). The 7% of participants who received only standard care had a case-fatality rate of 89.1%. 

Administering vaccines and using mAb114, REGN-EB3, and, to some extent, remdesivir further increase patient survival rates.

Patients who received the rVSV-ZEBOV vaccine were 1.7 times less likely to die than their unvaccinated peers (relative risk [RR], 0.59). This was the first outbreak outside of West Africa in which Ebola vaccine was widely used.

The risk of death rose 5% each day of treatment delay. Relative to standard care (no antiviral therapy), adjusted death rates were significantly lower after receipt of MAb114 (RR, 0.27), REGN-EB3 (RR, 0.26), or remdesivir (RR, 0.38). ZMapp patients also had a lower, albeit marginally significant, death rate (RR, 0.47).

"The high efficacy of MAb114 and REGN-EB3 compared to ZMapp and remdesivir in this analysis may partially explained by the fact that MAb114 and REGN-EB3 were administered as single doses, while ZMapp and Remdesivir required multiple infusions, which may have been delayed due to staff shortages or other operational barriers," the authors wrote.

"Prompt identification and treatment, along with enhanced supportive care (such as replenishing fluids and electrolytes and managing symptoms), significantly improve survival chances," they added. "Concurrently, administering vaccines and using mAb114, REGN-EB3, and, to some extent, remdesivir further increase patient survival rates."

An analysis of data from US hospitals in 2019 found that antibiotic treatment durations for uncomplicated gram-negative bloodstream infections (GN-BSIs) were longer than necessary, with marked variation among hospitals, researchers reported yesterday in Open Forum Infectious Diseases.

The observational study examined data on 4,240 episodes of GN-BSI (median patient age, 67 years; 51% male) at 24 US hospitals, all of which had antimicrobial stewardship programs. Half of the cases were uncomplicated, and 30% involved patients with compromised immune systems. The most frequent pathogens were Escherichia coli (53%), Klebsiella pneumoniae (21%), and Pseudomonas aeruginosa (8%). 

The median duration of antibiotic treatment for all GN-BSI episodes was 12 days, with 59% of cases treated for 10 days or more. In the uncomplicated and immune-compromised subgroups, the median treatment duration was 11 days and 13 days, with 51% and 67% treated for 10 days or more, respectively. At the individual hospital level, median treatment durations ranged from 7 to 14 days, with a similar pattern of variability observed in the uncomplicated and immune-compromised subgroups.

A logistic regression model that included only uncomplicated cases found that isolation of a non-Enterobacterales organism, isolation of a multidrug-resistant organism, and lack of intravenous to oral antibiotic switch at day 5 were independently associated with prolonged treatment.

'Substantial opportunity' to reduce treatment durations

The study authors say the findings are noteworthy, because randomized trials have demonstrated the effectiveness of 7 days of therapy for uncomplicated GN-BSI. In addition, most physicians and pharmacists reported in a prior survey that their preferred duration of therapy was 7 days. 

"Overall, our findings suggest there is likely substantial opportunity to reduce unnecessary variation in treatment durations for uncomplicated GN-BSI by promoting evidence-based, 7-day durations of therapy," they wrote. "This highlights the need to disseminate and scale successful interventions to reduce inappropriate variability in treatment durations."

• Over the past 2 days, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) reported 12 more H5N1 avian flu detections in dairy cattle, including 2 in Texas, its first since December 2024. The new detections push the number of affected herds in Texas since March 2024 to 29. The other 10 detections, reported yesterday, involve dairy herds in Idaho, which push the state's total to 100. Officials have now recorded 1,065 detections in dairy cattle from 17 states. In poultry developments, APHIS reported a few more detections, including a backyard flock in Maryland’s Anne Arundel County, a live bird market in New Jersey, and a commercial turkey farm housing 30,900 birds in Hutchinson County, South Dakota. The New Jersey health department said H5N1 was found in routine domestic poultry samples collected May 6. About 1,400 birds were depopulated at the market, which is temporarily closed.
• Brazil has reported its first H5N1 avian flu outbreak in commercial poultry, which began on May 12 near the city of Montenegro in Rio Grande do Sul, the country’s southernmost state, according to a notification today from the World Organization for Animal Health. The virus killed 7,389 of the 17,025 breeder poultry on the farm. Lab analysis found that the H5N1 virus belongs to the 2.3.4.4b clade, but the report did not list the subtype.
• Four countries reported more polio cases this week, all involving circulating vaccine-derived poliovirus type 2 (cVDPV2), according to the latest weekly update from the Global Polio Eradication Initiative. Burkina Faso reported its first case of the year, in a patient from Fada whose acute flaccid paralysis onset occurred on March 30. Ivory Coast's case involves a patient whose illness was reported in July 2024 and is recorded as the only case for that year. Ethiopia reported 5 cases in three states, bringing its total for the year to 21. Sudan reported 2 cases, 1 with a 2024 paralysis onset and 1 with a January 2025 onset. The cases mark the country's first for both years. Separately, Papua New Guinea's health ministry reported a polio outbreak after routine screening identified the virus in two healthy children, Euro News reported today. Wastewater sampling had detected the virus in Lae, the country's second-largest city.