From the article in Nature last year by the Cuban Apiculture Research group and Stephen Martin:

The mite infestation of worker cells currently varies between 23 and 13% in Cuba (this study), roughly 25 years after it was first detected (1996). Whereas, in Mexico and Brazil, infestation rates of worker brood have fallen from around 20% in 1996/1999 down to 4% in 2018/19. 

Those brood infestation numbers in US colonies would have them hurting, or be the precursors to much higher numbers and likely deadly outcomes.  So while there may be active mechanisms keeping the numbers at moderate or cycling levels, there is something different from what we see in the temperate regions.  It is intriguing that there are so many reports of coexistence between varroa and bees, but few say much about the actual levels in colonies through the seasons, untreated.

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