<prompt> B19 usually causes a very mild disease. Two groups of people for whom it can be serious, however, are?teenagers and pregnant womenpregnant women and sickle-cell anemicsthe sexually promiscuous and drug addictsalcoholics and asplenics  <response>: Primary infection in pregnant women is very serious and can result in death of the fetus. In patients with sickle-cell disease, the virus can initiate a transient aplastic crisis. Reference: Ananthanarayan and Paniker;s Textbook of Microbiology Tenth edition 