McDonald’s, 7-Eleven and mayonnaise-maker Kewpie are just some of the firms in Japan contending with the worst-ever global outbreak of bird flu.

Of 100 listed restaurant companies in Japan, 18 had suspended egg-related items as of Sunday, according to Teikoku Databank. Fewer hens led to a near-doubling in the wholesale price of the farm staple to ¥327 ($2.37) a kilogram in February from the year before, the research firm said on Tuesday.

That means McDonald’s Japan’s Teritama Muffin is off the menu. The breakfast sandwich, which combines egg, sausage and teriyaki sauce, is typically offered in spring each year. The fast food giant has also warned it could temporarily halt sales of hamburgers that contain eggs if supply disruptions persist.