Similar to the early results in the broader U.S. population, in the first few weeks of the vaccine rollout, we saw the vaccination rate for Black and Hispanic were approximately 40% below that of White and Asian American.
Our Hispanic patients have now been vaccinated at nearly the same rate as white patients and the gap for our black patients has been reduced to 10%.
On to our first quarter financial results.
We delivered solid performance in Q1 as our operating margins returned to 15.7% in the quarter, while we continue to lead through the continued challenges presented by the pandemic.
Our treatments per day hit a low point in mid-February, including the impact of approximately 25,000 missed treatments from the winter storm.
As of last Friday, the number of active cases among our patients across the country decreased approximately 85% from peak prevalence on January 6, 2021, and the last seven-day incidence rate for new cases decreased approximately 91% from the week ending January 9, 2021.
We've previously shared that the unfortunate incremental mortality associated with COVID was approximately 7,000 in 2020.
In the first quarter, incremental mortality associated with COVID was approximately 3,300 lives, with more than half of that number occurring in January, decreasing to approximately 600 in March.
However, now that the likelihood of some downside scenarios have decreased due to the trends I've previously mentioned, we are increasing our adjusted earnings per share guidance range to $8.20 to $9 per share and our adjusted operating income guidance range to $1.75 billion to $1.875 billion.
At the midpoint of our revised adjusted operating income guidance, this would represent approximately a 4% growth year-over-year.
It starts with the Board of Directors, currently made up of nine leaders, of whom 67% are diverse, including four women and three people of color.
The diversity of our team extends to the leaders who run the core operations in our clinics of whom 52% are female and 27% are people of color.
These reports disclose the progress we made in 2020 and lay out our ambitious ESG goals for 2025, including goals to reduce carbon emissions by 50% and to have vendors representing 70% of emissions set by climate change goals and to achieve engagement scores of 84% or higher among our teammate population.
For the quarter, we recorded revenue of approximately $2.8 billion, operating income of $443 million and earnings per share of $2.09.
As Javier referenced, treatment volume was a large headwind and our nonacquired growth was negative 2.2% compared to negative 0.3% in Q4.
While COVID presented the main challenge to NAG in Q1, winter storms, particularly Uri, were responsible for about 30 basis points of the NAG decline.
U.S. dialysis revenue per treatment grew sequentially by almost $3 this quarter as a result of the Medicare rate increase, higher enrollment in MA plans, a slight improvement in commercial mix and higher volume from our hospital services business, partially offset by the seasonal impact of coinsurance and deductible.
U.S. dialysis patient care costs declined sequentially by approximately $6 per treatment.
Although we continue to experience elevated costs due to the pandemic, such as higher PPE and certain clinical level expenses from continued infection control protocols, our Q1 patient care costs included a nearly $2 per treatment benefit from our power purchase agreement, a benefit that we do not expect to persist through the rest of the year.
For the quarter, the net headwind related to COVID was approximately $35 million, consisting primarily of higher PPE costs and the compounding effect of patient mortality associated with COVID, partially offset by the benefit from the sequestration suspension with a number of other items that largely offset each other.
For fiscal year 2021, we now estimate the net negative impact from COVID to be approximately $50 million lower than our guidance last quarter.
At the middle of our guidance range, this would equate to $150 million negative impact from COVID in 2021.
This quarter, we had more of these holes and the single largest driver was related to winter storm Uri, which impacted more than 600 of our centers until right in the middle of the quarter.
In the first quarter, we repurchased 2.9 million shares of our common stock.
Debt expense was $67 million for the quarter.
We expect quarterly debt expenses to increase to approximately $75 million beginning next quarter as a result of the $1 billion of notes issued in late February.

Summary:
On to our first quarter financial results.
However, now that the likelihood of some downside scenarios have decreased due to the trends I've previously mentioned, we are increasing our adjusted earnings per share guidance range to $8.20 to $9 per share and our adjusted operating income guidance range to $1.75 billion to $1.875 billion.
For the quarter, we recorded revenue of approximately $2.8 billion, operating income of $443 million and earnings per share of $2.09.