417 patients at UCSF Medical Center received an alarming letter warning them they they might have been exposed to diseases like Hepatitis B, Hepatitis C, and HIV after a medical device used for an internal examination was improperly cleaned.

UCSF sent the patients letters alerting them of the risk and offering them free blood tests for those infections, after a cystoscope used to examine their bladders was not properly cleaned from January 21 and June 26 of 2015, KRON4 reports.

According to the device's manufacturer, cystoscopes should be pre-cleaned with detergent, then a brush should be used to clean the inside of the scope's lens before sterilization is completed. That middle step, the one with the brush, was "completely skipped" during that five month period.

"It's concerning" Joshua Adler, UCSF's chief medical officer tells KRON4, "because it's a necessary step, it's a recommended step."

Adler says that the letters were sent to all exposed patients last week "even though the risk is low, if you were a patient, you'd want to know."

When asked why it took UCSF over a month to alert patients, he said that first staffers had to figure out which of the scopes weren't properly cleaned, then which patients were placed at risk.

So far, Adler says, only one patient has come in for testing, so it's too soon to say if anyone was infected by the unclean device.