Study finds wide variation in AAV hospitalization rates by country

Hospitalization rates for ANCA-associated vasculitis (AAV) vary substantially from one country to another, according to a multinational study.

Researchers examined hospital records from eight countries, including the U.S., between 2016 and 2022 and found that rates, subtypes, and in-hospital death proportions differed markedly, with Germany and England reporting the highest hospitalization rates and Mexico the lowest.

“Between-jurisdiction differences should be interpreted as comparative estimates of hospital burden rather than fully equivalent measures of underlying population [frequency],” the investigators wrote.

The study, “International variation in the hospital burden of ANCA-associated vasculitis: a multinational ecological analysis, 2016–2022,” was published in Autoimmunity Reviews.

AAV is a group of autoimmune conditions marked by damaging inflammation of small blood vessels throughout the body. The conditions fall into three AAV types: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA).

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Analysis uses hospital-based data

Early research has shown that AAV varies widely across geographies and ancestries. For example, GPA predominates in northern latitudes and Western populations, while East Asian regions show higher MPA rates. This suggests that population-specific genetic backgrounds and environmental exposures may contribute to these regional differences.

However, most of that evidence came from multinational clinical registries or national databases.

Researchers in Spain compared hospital-based data across eight countries using consistent methods to better understand how the hospital burden of AAV differs internationally. The team analyzed datasets from Spain, Germany, England, Wales, Chile, Mexico, Australia, and the U.S.

Among the more than 700 million hospitalizations recorded across these countries between 2016 and 2022, 116,039 (0.015%) were linked to AAV. GPA was the most common AAV type among these hospitalizations (63.6%), followed by MPA (25.6%) and EGPA (10.9%).

Females accounted for a slightly higher proportion of AAV-related hospitalizations in Spain (51.2%), Australia (52.7%), Chile (56.5%), and Mexico (59.6%), whereas males accounted for the highest proportion in Germany (52.7%) and England (50.7%).

Most hospitalizations occurred in AAV patients aged 15-64 in Spain (53.6%), Australia (58.2%), England (61.1%), Chile (69.1%), and Mexico (75.5%). Germany and Wales had the highest proportions of patients aged 65 and older (47.7%-49.6%).

Hospitalization rates varied widely. The crude rate (without age adjustment) ranged from 0.04 per 100,000 person-years (PYs) in Mexico to 9.61 per 100,000 PYs in Germany. PYs are combined measurement of the number of people in a study and the amount of time each person spends in that study.

Hospitalization rates were also high in England (7.87 per 100,000 PYs) and Australia (4.61 per 100,000 PYs), while lower rates were seen in Chile (0.80 per 100,000 PYs) and the U.S. (0.57 per 100,000 PYs). Spain’s rate was 1.75 per 100,000 PYs. Hospitalization rates were similar across AAV types.

Statistical analyses adjusted for age showed the same general pattern, with Germany, England, and Australia again showing the highest hospitalization rates, and Mexico and Chile the lowest. Likewise, sex-adjusted hospitalization rates also broadly mirrored the crude national rates. A similar pattern was observed across AAV types in analyses adjusted for age and sex.

Mortality data were available solely for Spain, the U.S., and Mexico. Among these countries, the U.S. reported the highest in-hospital death proportion for AAV (6.75%), followed by Mexico (4.66%) and Spain (1.48%).

A similar pattern was seen for GPA: 6.15% in the U.S., 4.55% in Mexico, and 1.29% in Spain. In-hospital mortality proportions for MPA were generally higher, at 7.75% in the U.S., 6.9% in Mexico, and 2.26% in Spain. EGPA-related mortality was highest in the U.S. (8.81%), with no deaths recorded in Mexico.

In Spain, being 65 or older was significantly linked to a higher likelihood of in-hospital death related to AAV, GPA, and MPA.

Trends over time also differed by country. AAV hospitalization rates significantly increased in Spain and Australia, while they decreased in Wales and Chile. The team found no significant changes in Germany, England, the U.S., or Mexico. MPA-related hospitalizations increased significantly in Spain and England.

These patterns largely held even after excluding data from 2020, the first year of the COVID-19 pandemic.

In-hospital death rates declined in the U.S. for overall AAV and GPA, while there were no significant changes in Spain or Mexico.

“This multinational analysis demonstrated substantial cross-jurisdiction variations in the AAV hospital episodes rates, [AAV type] distribution, temporal patterns, and in-hospital outcomes,” the researchers concluded. “GPA remained the predominant subtype and subtype-specific in-hospital mortality patterns varied across jurisdictions with available mortality data.”