Hello, The risks of oral sex are numerous. Unprotected oral sex can spread a variety of STDs, including herpes, syphilis, HPV, gonorrhea, and rarely, HIV. The direct and straight answer to your question is that he risk can t be quantified after getting a oral sex from a sex worker..there is no practical way to do so.The only way is to get tested for above mentioned diseases and since most of he tests are antibody based ,it takes many weeks to months to get proper results. During this time you are definitely putting your sexual partners at risk. Men who visit prostitutes are often particularly concerned about contracting HIV through oral sex. HIV can be transmitted through oral sex, although the risk of contracting HIV is much higher during other forms of sexual activity. However, since oral sex does include a risk of HIV, it is always a good idea to use a condom during oral sex -- particularly with an untested partner or a partner who is high-risk, such as a prostitute. Condoms are very effective at reducing HIV risk. However many commercial sex workers are very concerned about getting infected  and they try to practice safe sex and keep getting tested regularly. Don t get tense and get yourself tested. The chances of getting infected are very minimal but they do exist. Thanks.