Aetna is the latest health insurance provider to leave the Illinois health care exchange.

With Aetna's departure, there are just six insurers offering plans to individuals in 2017 and just two companies offering coverage to small businesses.

It is unclear how many people will be affected by Aetna's exit. Nationwide, Aetna covered some 838,000 people in health care exchanges during the second quarter.

Aetna joins UnitedHealthcare and the shuttering Land of Lincoln Health in exiting Illinois' exchange. Aetna claims higher than expected costs, particularly for specialty drugs, spurred the decision to leave the exchange.