Measles Update #4: Laboratory Error Resulting in a False Positive

We have just been informed by the PHOL, that because of a laboratory error, the positive result reported on March 12th was not correct and is in fact, negative for the measles virus. The PHOL is confident in the negative result. [...] Therefore, we now believe that the adult was not infected with measles, and that there have been no exposures to measles resulting from this person’s illness. We are working with the PHOL to reduce the risk of such an incident from occurring again. [...] Regardless, measles cases continue in other areas of the province. [...] The majority of Ontario cases reported in 2024 have been associated with travel (i.e. [...] Clinicians should continue to prioritize testing for symptomatic patients with the following risk factors: • Contact with a confirmed case; • International travel to areas with high-rates of measles; • Being unimmunized or partially immunized; • Being immunocompromised and/or pregnant. [...] Specimen Collection: • While the PCR test is highly sensitive and specific, it is essential that clinicians obtain as best as possible PCR specimens from all 3 sites in order to minimize the risk of false negatives and false positives: o Testing for measles should include three specimens for PCR analysis: 1. [...] Page 2 View all Public Health Alert bulletins at the Health Professionals Portal www.smdhu.org/HPPortal • Review the expiry dates of all specimen collection kits and ensure an adequate supply • Nasopharyngeal Viral Transport Medium and Throat Swab testing kits can be ordered from Public Health Ontario Laboratory • If serology is needed at a community lab, ensure infectious patients wait u [...] Infection Prevention and Control Primary care providers are encouraged to test clinically stable patients in their offices with appropriate IPAC precautions: • Schedule patients with compatible symptoms at a time that will minimize exposure of others (e.g., at the end of the day) • Immediately place patient in a single room with a door closed, negative air flow (airborne infection isolatio [...] • NEW: In addition to having immunity to measles (two doses of measles vaccination or laboratory evidence of immunity), all HCWs should wear a fit-tested, seal-checked N95 respirator when entering the room and/or caring for a patient with suspect or confirmed measles, given reports elsewhere of transmission of measles to HCWs with presumptive immunity. [...] (See Interim IPAC recommendations from Public Health Ontario) • Droplet/Contact precautions should also be used if the client has respiratory symptoms (gown, gloves and eye protection) • Following the patient’s visit, the exam room door must remain closed with signage to indicate that the room is not to be used for two hours.Page 3 View all Public Health Alert bulletins at the Health Prof