Background In resource-limited settings, where rubella is endemic, it is difficult to determine which sporadic case should be tested for rubella. The study aimed to provide useful evidence to help screen rubella cases for real-time reverse transcriptase-polymerase chain reaction (RT-PCR) examination for rubella in resource-limited settings. Method Suspected rubella patients identified by a physician and brought to the notice of the Ryugasaki public health center or the Tsuchiura public health center were enrolled from April 2018 through December 2019. The inclusion criterion was a confirmed rubella diagnosis based on laboratory tests. We studied the distribution of the time from the onset of fever until the onset of rash. Results The study included 86 cases with simultaneous presentation of fever and rash. Twenty-nine cases had confirmed rubella based on the laboratory diagnosis. Among these, the time from the onset of fever until the onset of rash was limited to − 1 day to 2 days. The number of rubella cases was the highest when the onset of rash was on the following day of the onset of fever. Of the 78 patients who underwent the RT-PCR test, 48% tested positive for rubella among those with a time from the onset of fever to the onset of rash between − 1 day and 2 days (22 out of 46, 95% confidence interval 34–62%); no positive results (0 out of 30, 95% confidence interval - 14%) were seen in patients with a time from fever to rash onset ≥3 days. Conclusion The period from the onset of fever to the onset of rash was limited to − 1 day to 2 days among confirmed rubella patients. If the period from onset of fever to the onset of rash was ≥3 days for a patient, the likelihood of rubella was low.

Background: In resource-limited settings, where rubella is endemic, it is difficult to determine which sporadic case should be tested for rubella. We investigated the period between the onset of fever, which is a prodromal symptom, and the onset of rash among laboratory-confirmed rubella patients. The study aimed to provide useful evidence to help screen rubella cases for real-time reverse transcriptase-polymerase chain reaction (RT-PCR) examination for rubella in resource-limited settings.Method: Suspected rubella patients identified by a physician and brought to the notice of the Ryugasaki public health center or the Tsuchiura public health center were enrolled from April 2018 through December 2019. The inclusion criterion was a confirmed rubella diagnosis based on laboratory tests. We studied the distribution of the time from the onset of fever until the onset of rash.Results: The study included 86 cases with simultaneous presentation of fever and rash. Twenty-nine cases had confirmed rubella based on the laboratory diagnosis. Among these, the time from the onset of fever until the onset of rash was limited to -1 day to 2 days. The peak in the number of rubella cases was on the day of rash onset, which was the day following the day of fever onset. Of the 78 cases who underwent the RT-PCR test, 48% tested positive for rubella among those with time from the onset of fever to the onset of rash between -1 day to 2 days (22 out of 46, 95% Confidence interval 34–62%); no positive results (0 out of 30, 95% Confidence interval 14%) were seen in patients with time from fever to rash onset ≥ 3 days. Conclusion: The period from the onset of fever to the onset of rash was limited to -1 day to 2 days among confirmed rubella patients. If the period from onset of fever to the onset of rash was ≥ 3 days for a patient, the likelihood of rubella was low.