Abbott Laboratories, the biggest U.S. supplier of powder infant formula including Similac, initiated a recall and closed its Sturgis, Michigan, manufacturing plant earlier this year after reports of serious bacterial infections in four infants.

The recall and shutdown has worsened a baby formula shortage among multiple manufacturers that began with pandemic supply chain issues.

Here are some details about what has happened:

WHEN DID THE PLANT CLOSE?

Production at an Abbott plant in Sturgis, Michigan, has been halted since February as the company works to rectify issues raised by federal inspectors.

WHY DID ABBOTT INITIATE A RECALL AND PLANT SHUTDOWN?

Consumers reported four infants who were sick, including three with Cronobacter sakazakii infections and one with Salmonella newport, and had been fed formula products made at the Sturgis plant. A fourth infant with cronobacter sakazakii was later added to the investigation by the U.S. Centers for Disease and Control Prevention.

Cronobacter sakazakii can cause life threatening sepsis infections or meningitis and may have contributed to the death of two of the infants, the U.S. Food & Drug Administration has said. It continues to investigate the four Cronobacter cases.

WHAT WAS RECALLED?

The recall began in mid-February with dozens of types of Similac, Alimentum and EleCare powdered formulas. A specialty liquid formula called Similac PM 60/40 was added to the recall at the end of February.

DID THE FDA OR CDC FIND A LINK?

Abbott says there is no evidence to link its formulas to these illnesses. The FDA and the CDC have not disclosed any information that connects the illnesses and the plant.

The U.S. Food & Drug Administration and Abbott tested environmental and product samples at the plant. They found five environmental samples containing Cronobacter sakazakii which Abbott says were in non-product contact areas of the plant. The product samples tested negative.

The CDC analyzed clinical samples from two of the infants and did not find a genetic match to the environmental strains found at the plant. It also said the bacteria from the patient samples were not closely related to one another.

WHEN WILL THE ABBOTT PLANT RESUME PRODUCTION?

Two experts Reuters spoke to expect the plant to resume production within two weeks. Peter Pitts, a former FDA head and President of the non-profit Center for Medicine in the Public Interest, said the issues were not mechanical and that Abbott and the FDA have been working to restart the plant for months.

Abbott has said it can open two weeks after it gets the go-ahead from the FDA. FDA Commissioner Robert Califf told NBC News on Monday it was "quite likely" there could be movement soon to reopen the facility.

Abbott has imported millions of cans of infant formulas from its Ireland facility to help with the U.S. shortage. The recall affected formula shipped to other countries, including Israel.

HOW LONG WILL IT TAKE FOR THE SHORTAGE TO SUBSIDE?

The shortages may last another two to four months even as lawmakers and the White House try to increase supplies. Abbott has said it will take six to eight weeks to get formula on shelves after the facility restarts.

U.S. food safety lawyer Bill Marler said even if the products are back in the market in the next two weeks there's still going to be a shortage for 30-60 days. "That's going to be difficult."

WHAT CAUSED THE SHORTAGE?

The shortage began in 2020 as consumers stockpiled due to COVID-19 lockdowns. Formula makers ramped up production but then cut back in 2021 as demand slowed. Global shipping logjams have also prevented retailers from promptly restocking shelves.

(Reporting by Manas Mishra, Leroy Leo and Deborah Sophia in Bengaluru and Richa Naidu in London; Editing by Ankur Banerjee, Caroline Humer and Sandra Maler)