In the latest Case Record of the Massachusetts General Hospital, a 35-day-old boy was admitted to the pediatric intensive care unit because of fever, vomiting, and severe anemia. On admission, he had signs of respiratory distress and tachycardia, with a heart rate of 176 beats per minute. A diagnosis was made.
Young infants with bacterial sepsis typically present with fever and abnormalities of the respiratory, gastrointestinal, and neurologic systems. Thus, evaluation in the emergency department with cultures of blood, urine, and cerebrospinal fluid, followed by antibiotic therapy, is appropriate.
• What are the common causes of bacteremia in young infants?
Bacteremia in young infants is most commonly due to Escherichia coli or group B streptococci. Staphylococcus aureus, particularly community-acquired methicillin-resistant S. aureus, is becoming a common pathogen but is usually associated with focal infections in bones, joints, or skin. Infection with Listeria monocytogenes, other enteric and nonenteric gram-negative bacilli, or viridans group streptococci occasionally causes sepsis in this age group.
• What is the characteristic clinical presentation of babesiosis?
Babesia infections may be asymptomatic, mild, or fulminant. The usual incubation period for an acquired tickborne infection is 1 to 6 weeks. On physical exam, fever is the most common feature. Splenomegaly and hepatomegaly may be present. Anemia with evidence of hemolysis on laboratory analysis is prominent, and thrombocytopenia is commonly present. Elevated liver enzymes are also common. Infection with B. microti is usually mild or asymptomatic but can be severe in infants, the elderly, asplenic patients, and immunocompromised hosts. Parasitemia may persist for months or years.
Morning Report Questions
Q: What other pathogens should one consider in a patient with a diagnosis of babesiosis?
A: It is important to consider the possibility of coinfection with other tickborne pathogens. Ixodes scapularis ticks may transmit Borrelia burgdorferi (the agent of Lyme disease) and Anaplasma phagocytophilum (the cause of human granulocytic anaplasmosis), in addition to B. microti. Of all patients with babesiosis, 12 to 53% have a history of Lyme disease or have positive tests for antibodies against B. burgdorferi, because a high percentage of ticks infected with babesia are coinfected with B. burgdorferi.
Q: What are the potential benefits of exchange transfusion in cases of high-level parasitemia?
A: Exchange transfusion is thought to have three benefits. First, exchange transfusion reduces the level of parasitized red cells, thereby leading to a decrease in hemolysis, in hypoxia, and in parasite replication. Second, it removes proinflammatory cytokines, tumor necrosis factor, and interleukin-1, which contribute to fevers, hemodynamic instability, and the development of the acute respiratory distress syndrome and multiorgan failure. Third, it is thought to improve rheologic properties of the blood, an effect that may improve end-organ perfusion.