How common is pelvic inflammatory disease? 
 Here is a information from United States.  Each year, more than 1 million women have an episode of pelvic inflammatory disease. More than 100,000 women become infertile each year because of pelvic inflammatory disease. Also, many ectopic pregnancies that occur are due to problems from pelvic inflammatory disease.

 Are some women more likely to get pelvic inflammatory disease?
Yes. You're more likely to get pelvic inflammatory disease if you:
• Have had an STI
• Are under 25 years of age and are having sex
• Have more than 1 sex partner
• Douche. Douching can push bacteria into the pelvic organs and cause infection. It can also hide the signs of an infection.
• Have an intrauterine device (IUD). You should get tested and treated for any infections before getting an IUD. This will lower your risk of getting pelvic inflammatory disease.

What if my partner is infected with pelvic inflammatory disease?
Even if your sex partner doesn't have any symptoms, she or he could still be infected with bacteria that can cause pelvic inflammatory disease. Take steps to protect yourself from being infected again.
• Encourage your sex partner(s) to get treated, even if she or he doesn't have symptoms.
• Don't have sex with a partner who hasn't been treated.