The head of the Food and Drug Administration said that the Abbott Nutrition plant in Michigan had a leaking roof, water pooled on the floor and cracks in key production equipment that allowedbacteria to get in and persist.

He detailed the unsanitary conditions in the plant to the lawmakers, but also acknowledged that his agency was too slow to respond.

The inspection results were shocking and the agency had no confidence in the quality program.

The facility is expected to reopen on June 4, according to an Abbott spokesman. New shipments will reach store shelves within six to eight weeks, but it will take longer to resume full production at the plant.

The leaking roof at the plant has been replaced by Abbott.

The House Energy and Commerce Subcommittee on Oversight and Investigations pushed back against the agency's assertions that it was difficult to recognize the extent of the contamination in real time. One-fourth of the nation's infant formula was produced by the Abbott plant.

There was a life-and-death crisis in front of the F.D.A., but they failed to see the severity of the situation.

Christopher Calamari, an Abbott Nutrition senior vice president, apologized for the shortages at the Michigan factory in his opening remarks. He said the company was coordinating 50 flights per week from its formula plant in Ireland to a dozen U.S. airports.

We are committed to making sure that this never happens again, Mr. Calamari said.

He said that the company is currently checking every step to make sure the quality checks are working in a sustainable way.

There were a number of problems at the plant last fall. Reports began to emerge of babies who had been hospitalized with a rare bacteria. According to the Centers for Disease Control and Prevention, Cronobacter sakazakii was found in four babies who had eaten formula from the plant.

The testimony made it clear that the F.D.A. took months to try to match the germs that were found in the first baby.

Dr. Califf testified to the House Oversight Committee about the Abbott Nutrition plant virtually on Wednesday.Credit...Brendan Smialowski/Agence France-Presse — Getty Images

The agency considers the Cronobacter strains that did not match the samples taken at the plant to be inconclusive.

The illnesses started the recall. The plant shutdown has left parents struggling to find baby formula and at times, they have to feed hungry infants.

The F.D.A. should have started its follow-up inspection in January, and it took too long to circulate a report that arrived in October, according to Dr. Califf.

It was too slow and there were decisions that were not optimal along the way.

The agency did not receive an immediate notice when the Cronobacter was found. The agency doesn't have access to the supply chain information that the baby formula manufacturers have.

During the hearing, the report of an anonymous employee who said he worked at the plant came up many times. The F.D.A. did not destroy enough product when it found Cronobacter in finished products, according to the whistle blower. Gary Palmer, a Republican from Alabama, said that the top agency leaders did not see the claims until February.

Representative Kim Schrier, Democrat of Washington, charged that there was corruption at the plant. Dr. Califf could not confirm or deny whether there would be criminal proceedings in the future.

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A growing problem. A nationwide shortage of baby formula has left parents confused and concerned. There are ways to manage uncertainty.

Finding a formula. If your baby's formula wasn't affected by the recall, you can call your local store and ask when it will be back in stock. You can buy it online. If your baby is on special formula, you should reach out to your doctor's office.

A new formula is being picked. If you use a name-brand formula, look for a generic version. If you want a new formula that matches your usual one, seek it. If your baby is on a special formula, make sure to check with your doctor.

A new product transition. You want to switch your child gradually. Gradually phase out the old product when you mix three quarters of your usual formula with one quarter of the new one. If you can transition gradually because you have run out of your usual formula, it's fine.

What not to do. If you can't find your baby's usual formula, don't make your own, homemade formulas are often inadequate and at risk of being contaminated. Don't try to stretch your formula by adding more water, and don't buy it from unvetted online marketplaces. Don't use toddler formula for a baby less than a year old.

The company could face heavy fines if it does not comply with the conditions of the consent decree. Cronobacter was found in finished baby powdered formula lots as far back as 2019.

The complaint concluded that Abbott officials have been unwilling or unable to implement sustainable corrective actions to ensure the safety and quality of food manufactured for infants.

Cronobacter sakazakii thrives in dry conditions. The New York Times has reported that only one state requires doctors or labs to report cases of food-borne illness from thebacteria to public health authorities, who in turn are supposed to alert the C.D.C.

The C.D.C. needs to change the protocols because they result in critical data gaps that undermine our ability to understand the true scope of Cronobacter infections in infants.

At the hearing, Dr. Califf agreed that reporting should be required.

The Defense Production Act was invoked last week by President Biden to increase formula production and to allow the use of aircraft to speed the shipment of infant formula. The first military plane carrying 500,000 bottles of formula arrived in Indianapolis on Sunday, and another was expected to land in D.C. on Wednesday.

The F.D.A. set up a streamlined process for foreign baby formula manufacturers to send their products to the United States. On Tuesday, it announced that it had approved a company's application to send two million cans.

Legislation signed by Mr. Biden expands the types of formula that can be purchased using benefits from the federal food aid program for women and babies, which cleared both chambers of Congress with few objections. A House-passed emergency measure to boost staffing for the agency, however, has stopped as some senators question whether the money will adequately address the shortage.

The top Republican on the Senate Committee on Appropriations said that they don't want anyone to be short of baby formula. Good government and market forces are the answer.

It's not clear what legislative steps Congress will take. Lawmakers hastily scheduled hearings to grill both Dr. Califf and top industry executives over the failures that led to the shortage. The Senate's Health, Education, Labor and Pensions Committee will hold a hearing on Thursday, with a panel of experts summoned by the House Appropriations subcommittees on Wednesday.

Emily contributed to the report.