There's a lot of talk about the possibility of a stock market crash. There's also increased volatility in the market, with rising concerns about the delta variant. However, the reality is that the stock market is still performing very well. The S&P 500 index is up nearly 16% year to date.

Some of the S&P 500 stocks that were the biggest winners in 2020 aren't faring nearly as well now. But others have taken their places. Here are three surprising stocks that have crushed the market so far this year.

Three blue lines with arrows pointing up.

Image source: Getty Images.

HCA Healthcare

Shares of HCA Healthcare (HCA 0.23%) have skyrocketed more than 50% so far in 2021. That's more than triple the return for the S&P 500 index. Why is the hospital chain having such a banner year? Chalk it up to a COVID-19 recovery.

HCA CEO Sam Hazen said in the company's recent second-quarter earnings call that HCA "experienced a strong rebound in demand for our services," thanks to a lower impact from the pandemic. Hazen noted that COVID-19 admissions in Q2 were only 3% of HCA's total admissions, compared to 10% in Q1.

Hospitals were hit hard last year during the worst of the pandemic. The biggest problem was that many more lucrative non-urgent surgeries had to be delayed. Those surgeries are no longer being pushed back, benefiting HCA.

Is HCA's strength only temporary? The company doesn't think so. It expects demand will remain strong throughout the rest of 2021. HCA also looks for growth in the demand for healthcare services beyond this year.

Idexx Laboratories

Idexx Laboratories (IDXX 0.78%) shares soared 90% last year. It didn't look like the veterinary-products stock would perform all that well for much of the first half of 2021, though. Idexx lagged behind the S&P 500 through early June. However, the stock is now up 34% year to date -- double the return of the major index.

The company's acquisition of ezyVet in June helped boost investors' confidence about Idexx's prospects. The deal enables Idexx to expand its cloud software offerings with ezyVet's practice information-management system for veterinarians.

Idexx projects that its revenue will increase between 14.5% and 16.5% for full-year 2021. The company's fortunes should be boosted by strong momentum in the companion-animal healthcare market, in particular.

The long-term opportunity for Idexx is enormous. The company estimates its global total addressable market size is around $33 billion annually. Idexx currently only serves roughly 5% of this potential market.  

Eli Lilly

It's unusual for big pharmaceutical stocks to crush the market. But that's exactly what Eli Lilly (LLY 3.17%) has done so far this year. Lilly's shares have vaulted more than 40% higher year to date.

Lilly has had a few setbacks, though. The U.S. Food and Drug Administration (FDA) pushed back its approval decision for Olumiant in treating severe atopic dermatitis to review additional data. Also, an FDA advisory committee overwhelmingly voted that Lilly's and Pfizer's proposed risk evaluation and mitigation strategy (REMS) for experimental painkiller tanezumab will ensure that the drug's benefits are greater than its risks.

Still, the good news for Lilly outweighed the bad news. Probably the most important of the company's positive developments was its decision to pursue accelerated approval for Alzheimer's disease candidate donanemab, based on phase 2 data. Lilly initially opted not to take this route, but changed its mind after the FDA approved Biogen's Alzheimer's disease drug Aduhelm.

The FDA's decision on accelerated approval for donanemab will no doubt be pivotal in whether or not Lilly's share price will continue to climb significantly. Even if the agency gives a thumbs down, though, Lilly could still have a path to approval with its ongoing late-stage study of the drug in treating Alzheimer's disease.