The tides have turned for the health care sector. In the second half of 2018, health careOpens a New Window. was the best performing sector in the S&P 500 indexOpens a New Window., rising 3.7 percent vs a 7.8 percent decline in the S&P 500. So far in 2019, with the market gaining upside momentum, health care has become the worst performing sector, advancing only 4.6 percent through Wednesday, while the S&P 500 is 11.9 percent higher.