Toronto's medical officer of health is speaking out against cuts the province is making to the city's public health budget.

Dr. Eileen de Villa says public health initiatives appear to be invisible when they work because they prevent disease, so it is easy to take them for granted.

She says public health units also play a key role in relieving the pressure on the province's primary care system by ensuring people don't become ill in the first place.

De Villa says changes to the cost-sharing between the city and province have left her at a loss for words.

The province notified health units late last week that it will reduce cost-sharing from levels of 100 per cent or 75 per cent, to 60 to 70 per cent for some municipalities.

In Toronto's case, the cost-sharing for some programs drops to 50-50 by 2021.

The city estimates that will mean a cut of more than $1 billion over a decade -- a figure the province has disputed.