Welcome to the twelfth edition of FOI Clinical. Each week, we'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Mpox (domestic) - Chikungunya - Coccidioidomycosis- VRSA in North Dakota - Petting zoo cryptosporidiosis in Rhode Island - Multi-state Salmonella Saintpaul - Rare disease reports - Mpox (international) - Avian influenza 

National interest

Measles

National measles continues its slow deceleration. The big milestone this week is in South Carolina.

• South Carolina: The Upstate outbreak was officially declared over on April 27, 42 days after the last outbreak-associated case. The final count stands at 997 cases and at least 21 hospitalizations, centered around Spartanburg County, with the vast majority in unvaccinated children.
• Utah: Now the state with the most active measles transmission in the country. The outbreak reached 625 cases as of April 28 (of which 428 have been recorded in 2026). The Southwest Utah health district near the Arizona border accounts for the largest share (260 cases), followed by Utah County (97) and TriCounty (71). Of those diagnosed, 531 (85%) were unvaccinated and 51 have been hospitalized. What started in small communities with low vaccination rates along the Arizona border has spread to every corner of the state. Since the outbreak began, MMR vaccine administrations in Utah have increased 31%. State kindergarten MMR coverage (88.6%) remains well below both the national average (92.5%) and the 95% herd immunity threshold.
• California: 46 confirmed cases this year.
• Texas: 180 cases this year as of April 22.
• Oregon: 2 new confirmed cases bringing the total up to 22 for the year.

The U.S. measles elimination status will be reviewed in November. No measles-related deaths have been confirmed in 2026, but 98 patients have been hospitalized (6% of cases). Among all cases this year, 92% are unvaccinated or have unknown vaccination status.

Mpox

Mpox activity continues to track above last year. Through the week of April 18, there have been 478 cases reported nationally, compared to 282 at the same point in 2025, a 1.7x increase. Six cases were reported the week of April 18.

California remains the epicenter for domestic clade II transmission, averaging 14.5 cases per week, up from 5.8 in 2024 and 3.4 in 2025. CDPH is strongly encouraging vaccination for high-risk Californians, following a clade I case in San Francisco in an unvaccinated resident who was hospitalized after close contact with an international traveler.

CDC continues to assess the risk to the general population as low, and to men who have sex with men (MSM) as low to moderate.

Chikungunya update

Chikungunya is running ahead of seasonal expectations. National year to date cases reached 147 through the week of April 18, well above the prior-year pace, with Florida accounting for 135 (92%). Weekly cases rose to 3, against a near-zero historical baseline for this point in the year. The ongoing Cuba outbreak continues to drive travel-associated cases into South Florida. Miami-Dade County confirmed one locally acquired case earlier this year and remains under a mosquito-borne illness alert as temperatures rise. As mosquito season begins, the risk of additional local transmission increases. The FDA-approved IXCHIQ vaccine is available for travelers to endemic areas.

Regional interest

Welcome to the eleventh edition of FOI Clinical. Each week, we'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Mpox - Chikungunya update - Rotavirus - Haemophilus influenzae - Legionellosis: early season signal - Mpox global update

National interest

Measles

As of April 16, 2026, there have been 1,748 confirmed cases of measles this year across 33 jurisdictions, up 34 from last week's 1,714. Nineteen outbreaks have been reported, and 94% of confirmed cases (1,637 of 1,748) are outbreak-associated. The weekly pace continues to slow.

• South Carolina: The outbreak centered around Spartanburg stands at 997 cases as of April 14, with no new outbreak-associated cases since March 17. The outbreak is set to be officially declared over on April 26, 42 days after the last case. However, a separate travel-associated case

Welcome to the tenth edition of FOI Clinical. Each week, we'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Mumps - Vector-borne disease season: Chikungunya and West Nile virus - Plague update – Trichophyton mentagrophytes genotype VII update - H9N2 - Mpox

National interest

As of April 9, 2026, there have been 1,714 confirmed cases of measles this year, up 43 from last week's 1,671, the smallest weekly increase of 2026. Thirty-three states have reported cases.

The deceleration should not be mistaken for the end of the resurgence. South Carolina's outbreak is effectively over with no new cases, and Florida has slowed. But Utah continues to accelerate, and Oregon is seeing a new cluster of locally acquired cases with no clear epidemiologic links, suggesting undetected community spread.

• South Carolina: No new cases since the

The 2025–2026 RSV season in the United States has followed an atypical trajectory. Elevated RSV activity did not begin until December 2025, and the season peaked in late February 2026, roughly 8 weeks later than the 2023–24 season. Peak hospitalization rates were lower than either of the two preceding seasons. As of late March 2026, RSV activity is declining nationally but remains elevated in several regions, particularly the Mountain West.

In response to the prolonged season, 48 of 66 federally funded immunization programs have extended nirsevimab (Beyfortus) eligibility through April 30, 2026.

Disease severity among hospitalized patients has been comparable to recent seasons. The shift is in timing, not in clinical presentation.

Welcome to the ninth edition of FOI Clinical. Each week, we'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Sexually transmitted Shigellosis - Typhus in California - Plague in New Mexico - Mpox in Germany

National interest

Measles

As of April 2, 2026, there have been 1,671 confirmed cases, up 96 from the week before. The largest case totals continue to be in South Carolina, Utah, Florida, and Texas, though Utah is currently a focal point for new transmission.

The rate of new cases has dwindled, with the South Carolina outbreak effectively over, and the outbreak in Florida slowed. However, this is not the end of the measles resurgence. New clusters will likely emerge in the weeks and months ahead.

• South Carolina: No new cases have been reported since the week of March 8. If no new cases are reported, the outbreak is approximately two weeks away from being declared over.
• Utah: Case counts are climbing rapidly in Utah. There have been 378 cases reported this year, bringing the outbreak total to 575. Another 60 cases were reported last week, double the number reported the week before. While the largest case totals continue to be in Southwest Utah (242), cases have been reporting in areas covered by 11 local health departments, including Utah County (87), Salt Lake County (60), TriCounty (56), and Central Utah (46). There have been more than two dozen exposure locations reported in the past few weeks, including at more than one Walmart location, multiple University of Utah buildings, and numerous clinics and hospitals.
• Texas: As of April 1, there have been 175 confirmed cases. All five of the new cases are associated with federal detention facilities in Hudspeth County (135 total cases have been reported so far in federal detention facilities in the county).
• Florida: New cases appear to be slowing in Florida; as of March 28, there were 144 confirmed cases, an increase of 1 from the week before. The vast majority of cases have been in Collier County (106); while 12 other counties have reported cases, the totals remain in the single digits.
• Arizona: The outbreak along the border with Utah continues, rising to 77 for 2026, and 291 for the total outbreak. 11 new cases were reported in the last week in March.
• North Dakota: As of April 1, 27 cases and 5 hospitalizations have been confirmed in the state this year. After several weeks with no reported cases, 5 were reported between March 23 and April 1, all in Ransom County. However, most cases so far this year in the state (23) have been associated with an outbreak in Pembina County. There have also been single cases reported in Williams, Traill, and Walsh Counties.
• Oregon: 13 cases have been reported in the state this year, 6 since the start of March. The state did not report any cases in 2024 or 2025. Most of the reported cases appear to have been locally acquired, but have not been epidemiologically linked to each other, which suggests there is ongoing community spread that is not being detected.

Sexually transmitted shigellosis

Shigellosis is increasingly being reported as spreading through sexual networks, particularly among men who have sex with men (MSM). The UK Health Security Agency recently reported that in 2025, there were 2,560 cases of sexually transmitted shigellosis, a higher rate than in either of the prior two years.

Case reports are not currently elevated in the United States, according to data from the National Notifiable Disease Surveillance System.

Infection with one of four species of Shigella bacteria produces shigellosis. It is spread via the fecal-oral route, and can be acquired through contaminated food, water, or surfaces or through direct contact. Importantly, particularly for sexual transmission, bacterial shedding in stool can continue for roughly two weeks after symptoms resolve.

Welcome to the eighth edition of FOI Clinical. Each week, I'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Mumps - Haemophilus influenzae - Tularemia in CA - Tetanus in CA - Hepatitis A in Italy

National interest

Measles

As of March 27, 2026, there have been 1,575 cases, up 88 from last week. The largest case totals continue to be in South Carolina, Utah, Florida, and Texas.

The rate of new cases has dwindled, with the South Carolina outbreak effectively over, and the outbreak in Florida slowed. However, this

Welcome to the seventh edition of FOI Clinical. Each week, I'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Seasonal respiratory illness update - Mpox in Missouri - Hantavirus pulmonary syndrome in New York - Leptospirosis in Ohio, territories - Meningitis in the UK

National interest

Measles

As of March 19, 2026, there have been 1,487 confirmed cases of measles this year. Thirty-two states have reported cases. The largest case totals are in South Carolina, Utah, Florida, and Texas.

Several notable outbreaks are underway. The list below is not comprehensive, but rather a selection of prominent active clusters worth keeping in mind.

• South Carolina: As of March 24, there have been 997 confirmed cases in a multi-county outbreak. There have been no new cases reported since the last edition of FOI Clinical.
• Arizona/Utah: The outbreak in Utah is growing quickly. There have been 486 confirmed cases, an increase of 38 from last week. All local health departments in the state have reported cases, with the majority of cases reported in Southwest Utah (n = 233), Utah County (n = 78), Salt Lake County (n = 53), and Central Utah (n = 36). The virus is present in wastewater samples around the state, confirming active community spread. Exposed locations are listed here. The outbreak in Arizona is growing more slowly; there have been 2 new cases reported in the last week, raising the total for the outbreak to 280.

Welcome to the sixth edition of FOI Clinical. Each week, I'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles - Seasonal Respiratory Infections - Interim Flu VE - Expanded RSV Vax Approval - Hantavirus in New Mexico - Infant Formula Recall Outside US - Meningitis in the UK

National interest

Measles

As of March 12, 2026, there have been 1,362 confirmed cases of measles this year, up 81 from the week prior. Thirty-one states have reported cases. The largest case totals are in South Carolina, Utah, Florida, and Texas.

Several notable outbreaks are underway. The list below is not comprehensive, but rather a selection of prominent active clusters worth keeping in mind.

• South Carolina: The multi-county outbreak in South Carolina has 997 confirmed cases to date. The outbreak has slowed considerably, with 7 new cases confirmed in the past two weeks.
• Arizona/Utah: The apparent slowdown over the past couple of weeks was a mirage. Cases have shot up in Utah, with more cases reported during the last week in February (44) than in any prior week in the outbreak (data reporting is a few weeks delayed for the state). This brings the total for 2026 to 209 and the outbreak total to 405, meaning more cases have now been reported this year than last year. More than 150 people (nearly 40%) have gone to the emergency department for measles during this outbreak, according to the state's epidemiologist. Exposed locations are listed here. Increasing vaccination rates is proving challenging, particularly in the heavily-affected southwestern part of the state. In contrast, Arizona has not reported any new cases in March, and the total remains at 276 for the outbreak.

Welcome to the fifth edition of FOI Clinical. Each week, I'll send you a briefing on outbreak news. When something urgent breaks, you'll get an alert the same day.

In this edition

Measles updates - H5N1 - Mumps - Seasonal respiratory viruses - Viral hemorrhagic fever

Measles

Latest epidemiology

As of March 5, 2026, there have been 1,281 confirmed cases, up 145 from the week prior. 31 states have reported cases so far this year. The largest case totals have been reported in South Carolina, Utah, Florida, and Texas.

Updates on Hotspots

Several notable outbreaks are underway. The list below is not comprehensive, but rather a selection of prominent active clusters worth keeping in mind.

Flu, Covid-19, and RSV vaccine effectiveness data for this season is starting to come in. FOI Clinical has pulled out the key numbers you need for patient counseling and end-of-season decision-making. These numbers can help you set realistic expectations with patients and answer the question, "did my flu shot even work?"

So far, effectiveness looks similar to a typical year, even with the emergence of the new H3N2 subclade K. As always, effectiveness depends on how well circulating strains match the vaccine composition.

Influenza

This season, adults: Canadian researchers estimated how well this season's flu vaccine is working against H3N2, the dominant flu strain circulating this season. Using data from four provinces, they found the vaccine reduced the risk of a doctor visit for H3N2 flu by roughly 40%. Like the United States, Canada predominantly uses egg-based vaccines.

This season, adults: UK Health Security Agency estimated around 75% effectiveness against

The Centers for Disease Control and Prevention (CDC) is investigating a multistate outbreak of extensively drug-resistant Salmonella infections linked to Rosabella brand moringa powder capsules distributed by Ambrosia Brands, LLC.

Seven cases have been reported across seven states, with three hospitalizations and no deaths as of February 13. The outbreak strain is resistant to all first-line and alternative antibiotics commonly recommended for Salmonella, and carries an NDM-1 carbapenemase gene, meaning it may also be resistant to carbapenems. According to CDC, this is the first documented outbreak of Salmonella with an NDM-1 gene in the United States.

The capsules are sold in white plastic bottles with a green label, covering 52 lot codes with 2027 expiration dates. The product was available nationwide primarily through the company's website, Amazon, TikTok Shop, Shein, and eBay. The firm has agreed to a voluntary recall. Specific lot codes are available on FDA's website.

This is

FOI Clinical is a resource from the team behind Force of Infection, trusted by 46,000 readers for flu, Covid-19, RSV, and norovirus tracking.

We track outbreaks and disease activity, then send you detailed reports on what's relevant to your practice. 

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In September 2022, Force of Infection gave early warning of what became the tripledemic. In October 2025, we warned that the 2025–2026 flu season was shaping up to be big. We gave readers weeks of lead time before it hit the news or their communities.

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