The United States has the worst healthcare system among 10 developed countries, according to the results of a poll released Thursday.

The study conducted by the Commonwealth Fund, a private foundation that has produced an annual report on health care rankings since 2004, found Australia, the Netherlands and the U.K. have the top three systems, but said, "Differences in overall performance between most countries are relatively small."

That excludes the U.S., however, which it said is "the only clear outlier" because its health care system performs "dramatically lower" than its peers.

"The U.S. continues to be in a class by itself in the underperformance of its health care sector," the report's authors wrote. "While the other nine countries differ in the details of their systems and in their performance on domains, unlike the U.S., they all have found a way to meet their residents’ most basic health care needs, including universal coverage."

The survey looked at the healthcare systems in Australia, Canada, France, Germany, the Netherlands, New Zealand, Sweden, Switzerland, the U.K. and the U.S. It evaluated them on the basis of access to care, care process, administrative efficiency, equity and health outcomes.

While no nation performed consistently well across all domains, the U.S. ranked dead last on access to care, care process, equity and health outcomes. It ranked ninth in administrative efficiency, better only than Switzerland.

Sweden was not included in the equity category because of changes to its privacy laws that prevented pollsters from asking income-related questions of respondents.

Affordability remains a major impediment for Americans seeking to access the country's health care system, which the report described as a "pervasive problem."

An estimated 26 million Americans lack any health care coverage while many others are underinsured owing to rising costs of deductibles in private insurance plans.

"Extensive cost-sharing requirements render many patients unable to visit a doctor when medical issues arise, causing them to skip medical tests, treatments, or follow-up visits, and avoid filling prescriptions or skip doses of their medications," it said.

That differs greatly from the U.K. where the National Health Service provides free universal health care, and in Germany, which caps deductibles based on a patient's income.