Reactive lymphocytes in patients with Covid-19.

From January 23 to February 27, 2020, Singapore had 96 Covid-19 cases confirmed by real time reverse transcriptase-polymerase chain reaction (RT-PCR) for SARS-CoV-2. We examined the peripheral blood films of 32 patients and found reactive lymphocytes as shown in the top images in 23 cases (72%). This is in stark contrast to the coronavirus responsible for the 2003 SARS outbreak where reactive lymphocytes of this type were not present in a review of 185 SARS cases in Singapore and were present in only 15.2% of 138 cases in Hong Kong (Chng et al., 2005; Lee et al. 2003).