MADRID—Spain has detected its first case of the Omicron variant of the coronavirus in a 51-year-old man who arrived from South Africa on Sunday after a layover in Amsterdam, Madrid’s regional health authority said on Monday as Spain’s overall infection rate rose. The microbiology unit at Madrid’s Gregorio Maranon hospital, which sequenced and confirmed the new variant, added in a separate post on Twitter that the patient was in fair condition with mild symptoms. The latest outbreak, first reported in southern Africa, caused a global flurry of border restrictions and flight route suspensions over the weekend amid fears of a return to uncontrolled contagion. The heavily mutated Omicron variant is likely to spread internationally and poses a very high risk of infection surges that could have “severe consequences” in some places, the World Health Organization (WHO) said on Monday. Spain’s rolling 14-day COVID-19 infection rate rose to 199 per 100,000 …