The Rational Clinical Examination
David L. Simel, Drummond Rennie
Malaria
David L. Simel
Make the Diagnosis: Malaria
Topics Discussed:
criterion standard comparisons (diagnostic tests), likelihood ratio, make the diagnosis, malaria, parasitemia, plasmodium falciparum, plasmodium ovale, plasmodium vivax, prior probability, reference standards
Excerpt:
"For clinicians who have not traveled to endemic areas, the magnitude
of malaria as a health problem is difficult to grasp. There are
an estimated 250 million annual cases of malaria infection worldwide,
and malaria kills nearly 1 million people per year, of whom most
are children.1 The heterogeneous prevalence in
existing studies requires that clinicians in endemic areas have an
appreciation for the local prevalence. Travelers to potentially
endemic areas should get advice about the presence of malaria and
the potential need for antimalarial prophylactic medicine from the
Centers for Disease Control and Prevention (CDC, http://www.cdc.gov/malaria/travelers/country_table/a.html),
but health care workers in endemic areas will need to get information
from local health experts to understand the point prevalence. Unless
cases are validated with objective tests, clinical diagnosis alone
may lead to overdiagnosis.No symptom, including the classic findings of fever, chills,
rigors, and headaches,is specifically diagnostic for malaria. A
diverse range of clinical syndromes results from malaria infections,
and the type of syndrome results from interactions between the infecting
parasite species, the immune status of the host, and the use and
timing of antimalarial drugs.4 Nonimmune patients
(such as children in endemic areas and travelers typically) manifest
an undifferentiated febrile illness with fluctuating paroxysms of
fever and rigors, accompanied by malaise, headache, myalgias, arthralgias,
pallor, mild jaundice, tender hepatosplenomegaly, anemia, and thrombocytopenia.
The presence of splenomegaly (LR, 3.3; 95% CI, 2.0-4.7)
or hepatomegaly (LR, 2.4; 95% CI, 1.6-3.6) in patients
of any age are the most useful findings. Skin pallor in children
(LR, 2.0; 95% CI, 1.2-2.8) is useful, although its presence
in adults conveys no additional information. Combinations of findings
(primarily in high prevalence areas) have been evaluated (Table
82-5), but their accuracy varies as a function of the geographic
settings. When the prevalence of malaria is high and alternative
diagnoses to malaria seem not to apply, most experts consider the
patient to have malaria when confirmatory tests are not available...."
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