FLINT, MI -- The Centers for Disease Control and Prevention says it offered to help the state root out the cause of a deadly Legionnaires' outbreak here, but was turned down by Michigan health officials, who "felt that they had the skills and resources needed to perform the investigation themselves."

The CDC statement was issued Thursday, Feb. 11, one day before the state of Michigan released more than 20,000 pages of documents related to the Flint water crisis, including notes from a March 2015 conference call about the Legionnaires' outbreak and its possible connection to the Flint water system.

From June 2014 until November 2015, 87 cases of Legionnaries', including nine deaths, were reported in Genesee County, but the county Health Department and state Department of Health and Human Services have struggled to determine a certain cause for the sky-high numbers.

Jennifer Eisner, a spokeswoman for DHHS, said her agency did not make a formal request for more help from the CDC until January because the state provided the county Health Department with what it needed -- state epidemiologists and additional staff to probe the outbreak.

Gov. Rick Snyder last month announced the Legionnaires' spike for the first time even though documents have shown county and state officials suspected a connection between the outbreak and Flint's water system for more than a year.

Kristen Nordlund, press officer for the CDC, said the federal agency was initially contacted by the county in February 2015 and provided technical assistance through phone calls and emails.

"Based on the available information, CDC felt that a comprehensive investigation was warranted and offered to further assist Michigan by providing epidemiologic and laboratory support from Atlanta or in Michigan," Nordlund said.

"When states determine that additional expertise, capacity or resources are needed, they may invite the CDC to assist with an investigation... (but) an official request must be submitted from the state.

"In this case, Michigan felt that they had the skills and resources needed to perform the investigation."

CDC finally deployed a team to Michigan this month and DHHS requested federal Legionella bacteria experts meet to discuss "strategies for identifying buildings at increased risk for Legionella growth and spread."

Eisner said DHHS is currently working with the county to "finalize an enhanced analysis of the 2015 (Legionnaires') data" and to develop guidelines with the county and CDC to reduce the risk for growing or spreading Legionella.

The investigation into the cause of the explosion in Legionnaires' cases in 2014 and 2015 has not been closed, Eisner said.

Speculation about the source of the outbreak was included in an April 9, 2015, email released by Snyder today, Feb. 12.

In that email from Jennifer Crooks, Michigan program manager for the EPA Ground Water and Drinking Water Branch, the federal official notes:

Miguel Del Toral, regulations manager in the EPA's Ground Water and Drinking Water Branch, said that

Soon after the city began using the Flint River as its water source in April 2014, officials here stepped up hydrant flushing in an effort to keep stagnant water out of the distribution system.

But Del Toral, who first sounded a warning about toxic lead in Flint's drinking water eight months ago, speculated that the flushing was also "stirring up the sediment in the pipes," causing a large chlorine demand and increasing the potential for Legionella to thrive.

An EPA official in the same meeting said the state was "currently figuring out a communication-with-the-public plan," but the Legionnaires' outbreak was never disclosed to the public until 11 months later.

Snyder has said he only learned of the Legionnaires' spike last month -- when he announced it publicly -- but others close to the governor, including Director of Urban Initiatives Harvey Hollins knew about a "significant uptick" in Legionnaires' cases in Flint long before last month's announcement, documents have shown.