Eight ZIP codes held top-tier concentrations of Medicare outlier providers for every single year between 2013 and 2023. Not most years. All eleven.

That kind of persistence doesn't happen by accident. When the same postal codes appear at the peak of the national Medicare payment distribution across an entire decade, the pattern stops looking like noise and starts looking like structure.

The Same ZIP Codes, Year After Year

ZIP code 93720 (Fresno, California) and ZIP 07083 (Union, New Jersey) both entered 2013 tied at the top, each with 10 providers whose total Medicare payments placed them in the national top 0.1%. From there, their trajectories diverged sharply. ZIP 07083 held its top-tier status for 6 consecutive years, through 2018, then dropped out. ZIP 93720 never left. It maintained top-tier status for all 11 years studied, from 2013 through 2023.

Six other ZIP codes matched that 11-year streak: 72205 (Little Rock, Arkansas), 11021 (Great Neck, New York), 95819 (Sacramento, California), 37203 (Nashville, Tennessee), 67214 (Wichita, Kansas), 93103 (Santa Barbara, California), and 77030 (Houston, Texas). For Medicare beneficiaries in those areas, the concentration of extreme-billing providers isn't a temporary phenomenon. It's a persistent feature of the local care landscape, which means patients in those ZIP codes face a structurally different risk environment than patients elsewhere.

The contrast with ZIP 29572 (Myrtle Beach, South Carolina) makes the point clearly. That ZIP had 7 top-0.1% providers in 2013, one more than ZIP 77030, but appeared in the top tier for only 3 years total, with no stretch of 5 or more consecutive years. High provider counts in a single year don't predict sustained concentration. The 8 ZIP codes that held on for all 11 years represent something qualitatively different.

ZIP 48073 (Royal Oak, Michigan) sits in between: 8 top-0.1% providers in 2013, top-tier status for 9 of the 11 years studied (2013 through 2022, excluding 2020). That near-continuous presence still signals a durable concentration, even if it didn't quite match the unbroken streaks of the top eight.

Where the Money Flows: Ophthalmology and Oncology Dominate

The specialty-level data from 2013 shows where extreme Medicare payments concentrate by discipline. Florida Ophthalmology stands out: 16 high-spend providers (defined as individuals exceeding $5 million in Medicare payments in a single year) generated $91,466,538 in total Medicare payments, the highest total of any state-specialty combination in the data. That works out to an average of $5,716,659 per provider.

For context, Texas had 14 high-spend Ophthalmology providers in the same year but generated only $39,733,942 in total payments, less than half of Florida's total despite having nearly as many providers. California's 13 high-spend Ophthalmology providers averaged $3,190,346 each, well below Florida's per-provider figure.

Iowa's numbers deserve attention. Six high-spend Ophthalmology providers in Iowa averaged $4,959,461 each in 2013, the highest average among all Ophthalmology states in the data. A small number of providers in a mid-sized state generating that level of per-provider payment is precisely the kind of signal that ZIP-level concentration analysis is designed to surface.

Florida's Hematology/Oncology picture adds another dimension. Nineteen high-spend providers generated $62,355,891 in total payments, averaging $3,281,889 each. That's a different cost structure than Ophthalmology, more providers at lower individual averages, but the aggregate exposure to Medicare is substantial.

Systemic Concentration, Not Random Variation

The persistence finding reframes how to think about Medicare billing risk. A single year of elevated payments in a ZIP code could reflect a new practice opening, a temporary coding anomaly, or a local demographic spike. Eleven consecutive years of top-tier status rules out most of those explanations.

At least 8 ZIP codes sustained top-tier concentrations across the entire study period. That's a systemic pattern. The geographic footprint is narrow but durable, and the financial exposure is concentrated in specialties, Ophthalmology and Oncology, where high per-procedure payments and volume-sensitive billing create the conditions for sustained outlier status.

What the data can't yet answer: Florida Ophthalmology providers averaged $5,716,659 per provider in 2013. Whether that average grew or contracted by 2023, and whether those providers cluster in the same ZIP codes identified as persistent top-tier concentrations, would tell us whether the geographic and financial risks are converging or diverging over time.