Differentials
Gram-negative sepsis
Rocky Mountain spotted fever (RMSF)
SIGNS / SYMPTOMS
Severe headache and petechial rash are present in most patients.
Rapid progression of disease.
INVESTIGATIONS
Positive serology using indirect immunofluorescence assay detects increased IgM levels at the end of the first week of illness and increased IgG levels by 7 to 10 days after the onset of illness in RMSF.
Enzyme-linked immunosorbent assay (ELISA), latex agglutination, and dot immunoassays can also be used in the diagnosis of RMSF.
Acute meningococcaemia
SIGNS / SYMPTOMS
Petechial rash, purpura, and meningitis may be seen.
INVESTIGATIONS
Cerebrospinal fluid (CSF) or blood culture with Neisseria meningitides.
Pneumonia
SIGNS / SYMPTOMS
Symptoms of respiratory distress and crackles/rales on auscultation.
INVESTIGATIONS
Chest x-ray shows infiltration, consolidation, effusions, and cavitation.
Oximetry shows hypoxia and respiratory acidosis.
Meningitis
SIGNS / SYMPTOMS
Headache and neck stiffness.
INVESTIGATIONS
Positive CSF culture.
Leptospirosis
SIGNS / SYMPTOMS
There may be no difference in signs and symptoms, although patients may be asymptomatic between phases of the disease.
INVESTIGATIONS
Sensitivity of blood cultures is low, and culture isolation requires special media and up to 6 weeks of incubation.
Indirect haemagglutination assay and IgM dot ELISA are specific for acute infections from leptospirosis.[90]
Heat stroke
SIGNS / SYMPTOMS
Non-specific signs and symptoms such as fever, hypovolaemia, hypotension, confusion, and erythema can occur in both entities.
INVESTIGATIONS
History of heat exposure is essential to the diagnosis.
Adrenal crisis
SIGNS / SYMPTOMS
Cutaneous hyperpigmentation, refractory hypotension, and hypoglycaemia may be present; hyponatraemia and hyperkalaemia may be present; desquamation is absent.
INVESTIGATIONS
Serum cortisol level <20 micrograms/dL (<552 nanomols/L), followed by adrenocorticotrophic hormone (ACTH) stimulation test.
Scarlet fever
SIGNS / SYMPTOMS
Pharyngitis, anterior cervical adenopathy, and fever precede characteristic scarlatiniform rash (diffuse, finely papular, 'sandpaper-like', erythematous rash that blanches with pressure). Rash begins on the trunk and may spread; it is accentuated in flexural creases (i.e., under the arm, in the groin, in the elbows) often with petechiae, producing red streaks known as Pastia's lines. Cheeks flushed 'scarlet' with circumoral pallor. Skin desquamation may occur 3-4 days after appearance of the scarlatiniform rash. Tongue may be inflamed with a white coating and prominent papillae ('strawberry tongue').
INVESTIGATIONS
No differentiating tests: differentiated on the basis of history and clinical examination.
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