COVID-19 Surge 2025: Understanding the XFG “Stratus” Variant

COVID-19 Cases Rising as New ‘Stratus’ (XFG) Variant Emerges: What Doctors Should Know

Authored by Dr. Lina Mansour, MD, Infectious Diseases Consultant
The summer of 2025 has brought a familiar, though unsettling, resurgence of COVID‑19—with a new protagonist: the XFG subvariant, nicknamed Stratus. From wastewater detection and test‑positivity spikes to shifts in clinical and public health landscapes, Stratus is rewriting the viral narrative. Yet, amid rising cases, the severity remains contained—offering both challenge and reassurance.

1. Emergence & Global Spread of Stratus (XFG)
First identified in Southeast Asia in January 2025, Stratus (XFG) is a recombinant variant born from two Omicron sublineages—LF.7 and LP.8.1.2. Its moniker, "Stratus," whimsically echoes its mixed structure—likened by some to Frankenstein’s creation.

By late June, XFG comprised around 14% of U.S. cases, ranking third behind other Omicron offshoots like NB.1.8.1 (“Nimbus”) and LP.8.1. Globally, its share of cases reached 22.7%, according to WHO data, and WHO currently lists XFG among variants under monitoring—not yet a variant of high concern .

2. Current Trends: Rising Cases Across the U.S.
Texas

• Wastewater surveillance indicates a “very high” level of COVID‑19 activity statewide, with a spike accelerating since July.
  
  
• In the week of August 10–16, Texas reported a ~24% increase in probable or confirmed cases despite overall downturn in formal tracking systems.
  
  
• Stratus now makes up 71% of U.S. wastewater‑detected cases, signaling its dominance.
  

California & the Bay Area

• In California, test positivity has climbed to 11.6% statewide, with wastewater data showing high viral loads across regions.
  
  
• In the Bay Area, XFG has become the predominant strain, accounting for ~82% of variants detected in select sewage sampling sites.
  
  
• Earlier in the summer, cases soared—with Los Angeles County positivity around 12.6%, and Orange County up to 14.5%.
  
  
• Kern County (Central California) also reports rising wastewater virus levels, with local families reporting headaches, body aches, and loss of taste and smell.
  

Other U.S. States
CDC surveillance signals rising test positivity as high as 15% in Southern states, with national levels around 9.9%. A wide spectrum of states—including Texas, Louisiana, Missouri, Arizona, and beyond—are following similar trends.

3. Clinical Presentation & Patient Impact
Stratus symptoms are familiar to clinicians, mirroring prior Omicron offshoots, though with some nuances:

• Common symptoms: Fever, cough, congestion, fatigue, headache, sore throat, muscle aches, loss of taste or smell.
  
  
• Many patients report a particularly harsh, hoarse, or scratchy sore throat, reminiscent—but often milder—than the notorious “razor‑blade throat” of the Nimbus variant .
  
  
• Gastrointestinal symptoms (nausea, vomiting, diarrhea) and hoarseness are more frequently observed, though most cases remain mild.
  
  
• There’s no current indication that XFG leads to increased severity—hospitalizations, though rising among seniors and children, remain well below previous summer surge peaks.
  
  
• Some hospital admissions—especially pediatric—are attributed to children returning to school and expanded social contacts.
  
  Respiratory Symptoms
  • Sore throat/“razor-blade throat”: scratchy, painful, hoarse, variable severity.
    
    
  • Persistent cough: dry/tickly, throat-driven.
    
    
  • Nasal congestion/rhinorrhea: longer-lasting than colds/flu (up to 10 days).
    
  Systemic Symptoms
  • Fever/chills: moderate, more common in kids and elderly.
    
    
  • Fatigue/malaise: universal, lingers after recovery.
    
    
  • Myalgia/arthralgia: influenza-like aches, sometimes localized.
    
  Neurological & Sensory
  • Headache: frontal/retro-orbital, pressure-like.
    
    
  • Anosmia/dysgeusia: partial, transient, altered taste.
    
    
  • Brain fog: confusion, slowed thinking, word-finding issues (esp. elderly).
    
  Gastrointestinal
  • Nausea/vomiting: often in children, may precede respiratory signs.
    
    
  • Diarrhea: watery, self-limiting in 2–3 days.
    
    
  • Abdominal pain: cramping, mimics foodborne illness.
    
  ENT & Laryngeal
  • Hoarseness/voice changes: common, even without severe throat pain.
    
    
  • Ear fullness/tinnitus: transient, linked to Eustachian tube congestion.
    
  Pediatric Patterns
  • High fevers and croup-like cough (sometimes stridor).
    
    
  • Frequent GI symptoms.
    
    
  • Rapid spread in school outbreaks.
    
  Elderly & High-Risk
  • Exacerbations of chronic conditions (COPD, CHF, asthma).
    
    
  • Delirium and dehydration as presenting features.
    
    
  • Higher hospitalization risk.
    
  Comparative Severity
  • More ENT-dominant than earlier Omicron.
    
    
  • More GI symptoms, especially in children.
    
    
  • Return of anosmia/dysgeusia, shorter-lived.
    
    
  • Less severe pulmonary disease than Delta; pneumonia rare in healthy hosts.
    
  Timeline
  • Incubation: 2–4 days.
    
    
  • Onset: congestion/throat pain first.
    
    
  • Peak: days 2–5, resolution by day 7.
    
    
  • Long COVID: fatigue/dysautonomia in 10–15%.
    
  ✅ Clinical takeaway: Stratus is defined by ENT prominence (sore throat, hoarseness), GI frequency, transient sensory loss, and varied presentations in children and elderly. Recognizing these nuances helps distinguish it from influenza and seasonal infections.
  

4. Virology & Immunological Considerations

• Stratus’s recombination origin from LF.7 and LP.8.1.2 likely enhances transmissibility and immune evasion modestly .
  
  
• Its spike mutations may facilitate rapid spread, yet current vaccines continue to protect effectively against severe disease.
  
  
• Omicron‑based vaccine updates from late 2024 remain protective, but newer 2025‑26 versions face delays or access restrictions, especially for healthy younger adults and children.
  
  
• Instead, guidance now focuses vaccinations on high‑risk groups—while medical societies like the AAP and ACOG continue advocating broader coverage for children and pregnant individuals .
  

5. Surveillance & Public Health Messaging

• Wastewater surveillance has re‑emerged as a cornerstone tool for early detection—often preceding clinical testing metrics by days to weeks—and is critical for early intervention.
  
  
• Testing infrastructure remains spotty, with many infections going unreported due to at‑home tests.
  
  
• Public health communication is fragmented: some regions advise masking in crowded settings; others have shifted to recommending testing only for high-risk groups.
  
  
• Clinician-led education and clear guidance are vital to navigating evolving policies and patient expectations.
  

6. Clinical Guidance for Physicians

1. Maintain high clinical suspicion during summer-linked symptom spikes—especially sore throat or hoarseness in children and returning students.
   
   
2. Use wastewater trends and regional surveillance data to anticipate local clinical surges.
   
   
3. Continue to test symptomatic patients, advise isolation per current protocols, and manage with supportive care and antivirals if high risk.
   
   
4. Boost vaccination campaigns among eligible groups—particularly seniors, high-risk individuals, pregnant people, and young children—as vaccines still mitigate severe outcomes.
   
   
5. Encourage the use of masking in crowded settings, especially in schools and healthcare facilities.
   
   
6. Educate on symptom management—hydration, NSAIDs, throat soothers—and monitor for red-flag signs like difficulty breathing or persistent severe symptoms.
   
   
7. Report cases of unusual presentation or severity to public health bodies to refine understanding of evolving pathology.
   
   
8. Collaborate across specialties (pediatrics, obstetrics, primary care) to ensure consistent messaging.