Hi Kaitlin,

times to times we have such problem with our virus production, usually mycoplasma. There are many possible sources, difficult to say. Just be sure you follow all security guidelines. If contamination is there - something is wrong. (might be useful to check GMP standards for cleanroom). To prevent contamination - once a week we clean up our incubators and hoods completely, cell media is individual for each person in lab, if it contains serum - serum-batch is tested before, despite it heat-inactivated. Antibiotics are always included. Sterile tools, all surfaces always exposed to 70% ethanol before the use. 30-min to 1 hour UV overnight. Virus-containing supernatant is filtered before ultracentrifugation. Keep windows always closed, change shoes... lab coat reduce the release of colony forming units of human body from 5000 to 1200/min... etc. Keep it in mind.

good luck!