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sputumor tracheal secretion aspirate research can already present the proper
sensitivity to give us a diagnosis with the use of the culture, eliminating the
need of invasive procedures with bronchoscopy or lung biopsy.
Another quick and easy test to make the diagnosis is the detection of
urinary antigenof
Legionella
. Asmall urinary sample can reveal the antigenic
presence that persists for days even with the previous use of antimicrobials.
It is worth to remember some of the problems of this test. The test detects
only the
Legionella
antigen belonging to the serogroup 1 (there are 16
serogroups). So, we will only identify the infections in this serogroup. The
great advantage is that more than 90% of
Legionella
pneumonias derive
from this serogroup 1. Then the search of
Legionella
urinary antigen is a
valid test and helps our diagnosis with sensitivity oscillating between 70 and
80%. The description above explains why the sensitivity does not approach
100%, together with another reason. The greater the chance of positivity of
the urinary antigen, the greater the severity of the pneumonia, according to
the culture. As a result, negative culture or test for negative urinary antigen
does not exclude
Legionella
pneumonia.
The serology for
Legionella
does not help much in the medical practice
because the serological conversion occurs until the fourth week of the
infection. So, a new serological sample is required after four weeks to
evidence the positivity.
We find a great amount of diagnostic material in the recent tests to detect
bacterial genetic material. The NAAT (nucleic acid amplification test) in the
pulmonary secretion helps in the diagnosis of
Legionella
, but the limiting
factor is all the required laboratory devices, and the elevated cost.
