In December, I traveled to the United States for a family gathering. While there, オミクロンに感染しました (omikuron ni kansen shimashita, I caught the omicron variant).
Once I learned about my situation, I immediately got in touch with any 濃厚接触者 (nōkōsesshokusha, close contacts) to apologize for 迷惑をかける (meiwaku o kakeru, causing an inconvenience) to them.
In Japan, if you catch the 新型コロナウイルス (shingata koronauirusu, novel coronavirus) and think you may have been in close contact with someone, then you need to let them know and offer some kind of apology for causing 迷惑 (meiwaku, trouble/inconvenience). If the person is a family member or friend, then a quick text or phone call should do: コロナになってしまいました。もしかして感染させてしまったかもしれません。すみません (Korona ni natte-shimaimashita. Moshikashite kansen sasete-shimatta kamoshiremasen. Sumimasen, I’ve got COVID-19. You may have been infected. I’m sorry).