HOUSTON, Aug 12 (Reuters) - Top oilfield services firm Schlumberger NV (SLB.N) on Thursday said it had withdrawn staff from next week"s Offshore Technology Conference (OTC), which typically attracts at least 60,000 attendees to Houston, citing the area"s rise in COVID-19 cases. The annual exhibition and technical exchange for offshore energy equipment and service companies historically ranks among the 10 largest trade shows by attendance, attracting exhibitors and energy professionals from around the world. Last year"s conference was canceled due to the pandemic and this year"s event was pushed back from its usual spring schedule because of COVID-19. It will include in-person and broadcast programs. "As the Houston area hospitalization rates increase rapidly, Schlumberger has taken the decision to withdraw from the Offshore Technology Conference," spokeswoman Moira Duff said. The company is developing virtual presentations for the event, she added. Houston has been hit by a surge in the Delta variant, with some 3,422 people testing positive on Wednesday, from just 398 new cases a month ago. Harris County, which includes Houston, last week raised its alert level to its highest and asked unvaccinated residents to stay home. The city"s hospital complex, Texas Medical Center, this week said its Phase 1 intensive care units were full and a combination of Phase 1 and 2 two beds, which include additional ICU capacity, were 85% full as of Wednesday. An OTC spokeswoman did not have an immediate response to Schlumberger"s withdrawal. The program this year includes extensive safety measures in the conference hall and was designed to allow for in-person or online attendance, she said. Other companies, including engineering and construction firm McDermott International (MCDIF.PK), have reduced staffing and lowered their expectations for attendance. While the trade show drew 59,200 people two years ago, the number is likely to be down significantly this year. "We will have minimal personnel on-site," said Gentry Brann, senior vice president at exhibitor McDermott International Ltd. The firm continues to evaluate conditions and is "prepared to take further precautions to ensure the well-being of our people."