Consumers around the U.S. have noticed something missing from their grocery stores as they do their pre-Thanksgiving shopping: eggs. 

Some shoppers looking for eggs were greeted with signs apologizing for the food's absence — and some may be wondering why.

Egg production dropped 2.6% last month compared to October 2023, the U.S. Department of Agriculture (USDA) said in a recent report. 

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As it turns out, there's one big thing impacting egg availability: an outbreak of avian flu. 

Highly pathogenic avian influenza (HPAI) A(H5) viruses have been found in birds in the U.S. since January 2022, according to the USDA's website. 

Since the virus was first detected in the U.S., it has spread to 49 states.

More than 100 million birds have been affected, the agency said.

Other stores have cited non-flu reasons as to why their egg stock is limited. 

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At a Trader Joe's location in Chicago, a sign explained the absence of eggs. The store was in the process of transitioning to "cage free only" eggs and supplies might be limited temporarily, the sign said.

A shopper posted a picture of the sign on a Trader Joe's Reddit page on Sunday, asking if other people had seen similar ones at their stores.

Responses from people around the country confirmed eggs were in short supply at their locations but without the reason given in Chicago.

Fox News Digital reached out to Trader Joe's for comment. 

Shoppers at Whole Foods Market locations have also reported egg shortages. 

A Reddit user posted on a page for Whole Foods Market employees saying they were told the shortage is "not due to the avian flu" but because of "trouble sourcing eggs that meet our high egg standards." 

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Another user said that one store had a limited stock of eggs and customers were restricted in the number that they could buy.

Fox News Digital reached out to Whole Foods Market for comment. 

With the egg shortage, some may be concerned if the eggs they already have at home are still good to use. 

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Lisa Steele, author of "Fresh Eggs Daily," a blog and cookbook about raising chickens, told Fox News Digital that it is very simple to tell if an egg is still good to use — even if the expiration date has come and gone.

To do this, simply pour a glass of water and drop in the egg. 

Eggs that sink to the bottom and stay there are still good, but any "floaters" should probably be tossed, she said.