. A 29-year-old man presents with a 4-day history of fever, headache with retro-orbital pain, severe musculoskeletal and lumbar back pain and rash. The symptoms began 3 days after he returned from a 2-week vacation to the Caribbean islands. The rash developed on his face before spreading over his trunk and extremities. The patient reports receiving appropriate vaccination, including hepatitis A virus vaccine, hepatitis B virus vaccine, and typhoid vaccine. Laboratory tests reveal normal kidney and liver function tests but leukopenia and thrombocytopenia. Which of the following organisms is the most likely cause of this infection?
A. LeptospiraAll the listed diseases can be acquired during travel, but the severe myalgias, skin rash, and thrombocytopenia are most consistent with dengue. Dengue fever is characterized by fever, severe frontal headache, retro-orbital pain, and severe musculo-skeletal and lumbar back pain. A macular or scarlatiniform rash develops within 3 to 4 days of the illness. Virtually all cases respond to conservative measures with bleeding, hepatitis, and myositis reported as potential rare complications. Dengue hemorrhagic fever is a more severe form of the disease. It is more common among infants and elderly people. It is characterized by increased vascular permeability with hypovolemic shock and thrombocytopenia with spontaneous ecchymoses and mucosal bleeding. Dengue is a mosquito-borne illness. Leptospirosis is a spirochetal disease that has two phases. The bacteremic phase is characterized by sudden onset fevers, rigors, headache, photophobia, and severe myalgias. Four to 30 days later, the immunologic phase ensues and is characterized by conjunctivitis, photophobia, retrobulbar pain, neck stiffness, diffuse lymphadenopathy, hepatosplenomegaly, and aseptic meningitis. The most severe form is called Weil disease; it is associated with up to 40% mortality and is characterized by high direct bilirubin and mild elevation in alkaline phosphatase and transaminase values, combined with a high creatine phosphokinase. Malaria is a parasitic disease usually caused by P falciparum. Patients present with influenza-like symptoms, jaundice, and in its most severe forms with obtundation and confusion. Hepatitis A causes markedly elevated transaminase values and jaundice. S typhi causes typhoid fever. Patients present with influenza-like illness with abdominal discomfort and constipation. Mild, bloody diarrhea could develop in some cases. The patient might develop small rose-colored macules called “rose spots” on the trunk, but thrombocytopenia is not a common feature of typhoid fever.