Differentials
Pneumonia, bacterial or viral
SIGNS / SYMPTOMS
Cough is productive.
INVESTIGATIONS
Chest x-ray usually shows areas of consolidation (increased radiodensity), whereas in human monocytotropic/monocytic ehrlichiosis (HME) and human granulocytotropic/granulocytic anaplasmosis (HGA), chest x-ray might show interstitial pneumonitis simulating a viral infection.
Viral infections are ruled out based on specific laboratory tests (i.e., antigen detection, serology, polymerase chain reaction).
Gastroenteritides, bacterial or viral
SIGNS / SYMPTOMS
Nausea, vomiting, and diarrhea are more prominent.
INVESTIGATIONS
Direct examination of stool may demonstrate polymorphonuclear neutrophils and/or blood.
Stool cultures and antigen detection confirm diagnosis.
Cholecystitis
SIGNS / SYMPTOMS
Right upper quadrant pain is usually localized.
INVESTIGATIONS
Right upper quadrant abdominal ultrasound may show inflammation and dilation of ducts in the area of the gallbladder.
Sepsis
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms.
INVESTIGATIONS
Positive blood cultures.
Rocky Mountain spotted fever
SIGNS / SYMPTOMS
Frequency of rash is much higher.
INVESTIGATIONS
Positive polymerase chain reaction or immunofluorescence antibody assay specific for rickettsial DNA.
Thrombotic thrombocytopenic purpura
SIGNS / SYMPTOMS
Thrombocytopenia and a purpuric rash.
INVESTIGATIONS
Peripheral smears show schistocytes.
Serum shows elevated lactate dehydrogenase.
Babesiosis
SIGNS / SYMPTOMS
Jaundice is more frequent due to hemolysis.
Can coexist with human granulocytotropic/granulocytic anaplasmosis (HGA) and/or Lyme disease. All 3 etiologic agents are transmitted by the same tick vector.
INVESTIGATIONS
Diagnosed in the acute phase by observing typical intraerythrocytic parasites in peripheral blood smear.
Polymerase chain reaction is available at research laboratories and is positive for Babesia microti DNA/RNA.
Serologic diagnosis is possible in convalescent period. Antibodies against B microti present.
Lyme disease
SIGNS / SYMPTOMS
Presence of erythema migrans.
Can coexist with human granulocytotropic/granulocytic anaplasmosis (HGA) and/or babesiosis. All 3 etiologic agents are transmitted by the same tick vector.
INVESTIGATIONS
Serologic diagnosis is possible in convalescent period. Antibodies against Borrelia present.
Western immunoblotting shows presence of Lyme-specific IgM and IgG.
Polymerase chain reaction positive for Borrelia.
T-cell lymphoma
SIGNS / SYMPTOMS
Lymphadenopathy is not short lived.
INVESTIGATIONS
Circulating lymphocytes do not start decreasing by third week of illness.
Tests for clonality: T-cell receptor rearrangements. However, in sporadic cases, lymphocytosis is severe enough to cause false-positives with this test, and follow-up testing is indicated.
Typhoid infection
SIGNS / SYMPTOMS
May be difficult to distinguish; however, gastrointestinal symptoms are more frequent.
INVESTIGATIONS
Blood and/or stool cultures positive for Salmonella enterica serovar S typhi or S paratyphi.
Malaria infection
SIGNS / SYMPTOMS
Travel history to endemic areas. Presence of cyclical fevers.
Jaundice is more frequent due to hemolysis.
INVESTIGATIONS
Diagnosed in the acute phase by observing typical intraerythrocytic parasites in peripheral blood smear.
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