Hello dear, Thank you for writing. Even though the majority of cases of cystitis is caused by bacteria, there are a number of cases where no bacteria is identified as a cause. There are two situations that may explain your condition: 1- The urine specimen was not representative of the urinary tract, maybe because: A- It was taken after you had urinated during the night B- The urine specimen wasn t fresh when it reached the lab (urine must be admitted to the lab within 1 hour or at least refrigerated) C- The urine specimen may have been contaminated (genitalia should be cleaned accurately). 2- There are distinct cases in which the causative agent cannot be isolated in routine cultures. This is true for microorganisms like: viruses, mycobacteria, chlamydia, fungi, schistosoma (nonbacterial cystitis) In my opinion you should take a second urine specimen for culture. If that comes negative as well, your doctors should consider special cultures and tests for above mentioned microorganisms. I hope this was helpful. Best wishes, Dr. Alma