Differentials
Malaria infection
SIGNS / SYMPTOMS
Residence in/travel from malaria-endemic region.
Inadequate or absence of malaria chemoprophylaxis.
Haemorrhage is uncommon in malaria infection.
INVESTIGATIONS
Giemsa-stained thick and thin blood smears: positive for Plasmodium species.
Rapid diagnostic tests: positive for Plasmodium species.
Real-time PCR: positive for Plasmodium species.
Dengue fever
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms, particularly early in the course.
Dengue fever is more common in urban settings as the mosquito vectors (e.g., Aedes aegypti) are more predominant in urban settings.
INVESTIGATIONS
Serology: positive IgM or IgG.
Nonstructural protein (NS1) detection: positive.
Reverse transcription-polymerase chain reaction (RT-PCR): positive.
Yellow fever
SIGNS / SYMPTOMS
Jaundice and transaminitis are more common.
INVESTIGATIONS
Serology: positive IgM or IgG.
RT-PCR: positive.
Chikungunya virus
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms, particularly early in the course.
A diffuse maculopapular rash and joint swelling may occur.
INVESTIGATIONS
Serology: positive IgM.
RT-PCR: positive.
Zika virus
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms, particularly early in the course. A diffuse maculopapular rash is common.
Virus is transmitted via mosquito vectors (e.g., Aedes aegypti) mainly in urban settings.
Haemorrhagic manifestations are rare.
INVESTIGATIONS
Serology: positive IgM.
RT-PCR: positive (narrow window during symptomatic disease). RT-PCR positivity is prolonged if tested on a urine sample.
Hantavirus pulmonary syndrome
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms in the prodromal stage.
Respiratory signs and symptoms (e.g., cough, respiratory distress) may develop in the late stages of the disease.
INVESTIGATIONS
Serology: positive IgM or IgG.
RT-PCR: positive.
FBC and blood film: atypical lymphocytosis; elevated polymorphonuclear leukocytes.
Typhoid fever
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms.
INVESTIGATIONS
Blood or stool culture: positive for Salmonella enterica.
Rickettsial diseases
SIGNS / SYMPTOMS
Includes murine and epidemic typhus, Rocky Mountain spotted fever (also known as Brazilian spotted fever), and other spotted fever group rickettsia.
Eschar is typical (atypical in Rocky Mountain spotted fever).
Lymphadenopathy may be present.
Discrete rash.
INVESTIGATIONS
Serology: positive for IgM or IgG for Rickettsia species.
Eschar PCR: positive.
Blood PCR: positive in some cases in early acute illness.
Measles infection
SIGNS / SYMPTOMS
Consider in unvaccinated individuals.
There are no differentiating signs or symptoms in the prodromal phase. Koplik's spots (red spots with bluish-white central dot) develop on buccal mucosa.
Rash typically starts on the face and spreads craniocaudally.
INVESTIGATIONS
RT-PCR: positive.
Serology: positive for IgM or IgG.
Leptospirosis
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms; however, a history of exposure may be helpful.
Exposure to contaminated water or soil contaminated by infected rodents.
More common in tropical climates.
In South America, leptospirosis is associated with exposure to both rural and urban rodents (e.g., Rattus norvegicus species).
INVESTIGATIONS
PCR: positive.
Serology: positive.
FBC: normal to high WBC.
Influenza infection
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms in the prodromal stage.
Respiratory signs or symptoms (e.g., cough, nasal congestion) are more common as disease progresses.
INVESTIGATIONS
Viral culture or RT-PCR: detection of seasonal influenza virus or viral RNA.
FBC: normal.
Sepsis
SIGNS / SYMPTOMS
There are no differentiating signs or symptoms in the early stage of the disease process.
Bacterial sepsis with an unclear origin is a common presentation in developing countries.
INVESTIGATIONS
Blood cultures: positive.
PCR for specific bacteria: positive.
Coronavirus disease 2019 (COVID-19)
SIGNS / SYMPTOMS
Residence in/travel to a country/area or territory with local transmission, or close contact with a confirmed or probable case of COVID-19, in the 14 days prior to symptom onset.
INVESTIGATIONS
RT-PCR: positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA.
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