An expatriate businessman has described how he was robbed of HK$29,500 by an African prostitute in the latest incident of a reveller being drugged in Wan Chai. The man, who lives in Kennedy Town and does not want to be named, said the money - HK$500 short of his daily limit - was withdrawn from an ATM, but he has no clear recollection of carrying out the transaction. 'There's no doubt that I was drugged and taken to an ATM where I took out the money,' he said. 'I didn't know what I was doing but the woman was with me. It must have been an ATM she had used before for this purpose because she thought it was safer. I've only a vague recollection of the whole thing.' Four other men have contacted the Sunday Morning Post this year to say their drinks were spiked in Wan Chai. Each had iPhones and money stolen; the last thing any of them could recall was drinking with an African prostitute in a bar before feeling unwell. The latest victim, who works in the financial industry, said the woman knew exactly what she was doing by asking him to take out HK$29,500 as the daily cash limit is HK$30,000. He said he had been drinking and chatting with her in the Neptune II bar and soon became disorientated. He has vague memories of being in a taxi and at the ATM with her. He woke up in another bar and, when he tried to withdraw money later, he found he had reached his limit. Pub landlords in Wan Chai said the number of African sex workers in the area had at least doubled to about 20 in recent months. Police said 25 prostitutes were arrested in crime sweeps in the area over the past few weeks, some of these from Africa. In five operations this year police made 67 arrests - 57 foreign visitors and 10 Hong Kong residents. They were arrested for soliciting or breaching their condition of stay by working on a holiday visa. African prostitutes are in the minority and these incidents are recent occurrences. Most migrant sex workers are from mainland China. The most infamous incident of this type was when 'date rape' drug Rohypnol was a factor in the January 2003 death of policeman Kari Juhani Koivuniemi, 45, a chief superintendent from Finland. He suffered a heart attack at the Island Shangri-la hotel. Police investigated the case as murder, but it was never solved. Koivuniemi was last seen with an unidentified Asian woman, believed to be a mainland prostitute. Tony Liu Kit-ming, chairman of the Police Inspectors' Association, said he believed the police were doing as much as they could. 'The ethnic background of these sex workers does not matter. If they break the law, we will do something about it.'