The atypical pneumonias: clinical diagnosis and importance.
Clin Microbiol Infect. 2006
May;12 Suppl 3:12-24.
The most common
atypical pneumonias are caused by three zoonotic pathogens, Chlamydia
psittaci (psittacosis), Francisella tularensis (tularemia), and
Coxiella burnetii (Q fever), and three nonzoonotic pathogens,
Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella. These
atypical agents, unlike the typical pathogens, often cause
extrapulmonary manifestations. Atypical CAPs are systemic infectious
diseases with a pulmonary component and may be differentiated
clinically from typical CAPs by the pattern of extrapulmonary organ
involvement which is characteristic for each atypical CAP. Zoonotic
pneumonias may be eliminated from diagnostic consideration with a
negative contact history. The commonest clinical problem is to
differentiate legionnaire's disease from typical CAP as well as from
C. pneumoniae or M. pneumonia infection. Legionella is the most
important atypical pathogen in terms of severity. It may be clinically
differentiated from typical CAP and other atypical pathogens by the
use of a weighted point system of syndromic diagnosis based on the
characteristic pattern of extrapulmonary features. Because
legionnaire's disease often presents as severe CAP, a presumptive
diagnosis of Legionella should prompt specific testing and empirical
anti-Legionella therapy such as the Winthrop-University Hospital
Infectious Disease Division's weighted point score system. Most
atypical pathogens are difficult or dangerous to isolate and a
definitive laboratory diagnosis is usually based on indirect, i.e.,
direct flourescent antibody (DFA), indirect flourescent antibody (IFA).
Atypical CAP is virtually always monomicrobial; increased IFA IgG
tests indicate past exposure and not concurrent infection. Anti-Legionella
antibiotics include macrolides, doxycycline, rifampin, quinolones, and
telithromycin. The drugs with the highest level of anti-Legionella
activity are quinolones and telithromycin. Therapy is usually
continued for 2 weeks if potent anti-Legionella drugs are used. In
adults, M. pneumoniae and C. pneumoniae may exacerbate or cause
asthma. The importance of the atypical pneumonias is not related to
their frequency (approximately 15% of CAPs), but to difficulties in
their diagnosis, and their nonresponsiveness to beta-lactam therapy.
Because of the potential role of C. pneumoniae in coronary artery
disease and multiple sclerosis (MS), and the role of M. pneumoniae and
C. pneumoniae in causing or exacerbating asthma, atypical CAPs also
have public health importance.
Determination of serologic markers against bacterial atypical
pneumonia agents in pneumonia patients. Mikrobiyol
Bul.2004 Jan-Apr;38(1-2):27-32.
Approximately one
third of all community acquired pneumonia cases are caused by
Legionella pneumophila, Mycoplasma pneumoniae and Chlamydophila
pneumoniae (previously, Chlamydia pneumoniae) which are known as
bacterial atypical pneumonia agents. Serological tests are used
commonly for laboratory diagnosis of these agents. The aim of this
study was to evaluate the causative role of bacterial atypical
pneumonia agents in clinically diagnosed pneumonia patients. Acute and
convalescent serum samples were collected from a total of 65
clinically diagnosed adult pneumonia patients in order to evaluate IgM
and IgG positivities against L. pneumophila, M. pneumoniae and C.
pneumoniae. IgM and IgG were evaluated by enzyme immunoassay (ELISA)
for L. pneumophila and M. pneumoniae, and by indirect fluorescent
antibody (IFA) method for C. pneumoniae. In acute serum samples, 4
(6.2%) M. pneumoniae IgM positivity in addition to 3 (4.6%) L.
pneumophila IgG, 3 (4.6%) M. pneumoniae IgG and 62 (95.4%) C.
pneumoniae IgG positivity were detected. In convelescent serum
samples, 3 (4.6%) L. pneumophila, 1 (1.5%) M. pneumoniae, 3 (4.6%) C.
pneumoniae IgM positivity and 4 (6.2%) L. pneumophila with 1 (1.5%) M.
pneumoniae IgG positivity were detected in addition to acute sample
positivities. According to these serological data, totally 16 (24.6%)
of the patients were infected by bacterial atypical pneumonia agents.
These results show that bacterial atypical pneumonia agents are
important etiological factors for community acquired pneumonia.
Atypical pneumonia. Orv Hetil.2005 Aug
21;146(34):1759-66
International
epidemiologic surveys show that apart from community acquired
"typical" pneumonia the number of cases caused by atypical pathogens
are increasing. A number of problems are to be faced while diagnosing
and treating the lower respiratory tract infections due to atypical
pathogens. The article gives a detailed overview of pneumonia caused
by Chlamydia pneumoniae, Chlamydia psittaci, Mycoplasma pneumoniae,
Coxiella burnetti and Legionella species, and emphasizes that these
pathogens should be considered and thought about more in lower
respiratory tract infections as appropriate treatment, if started in
time, decreases the risk of a more severe outcome.
The other
causes of 'atypical' pneumonia.Curr
Opin Infect Dis. 1999 Apr;12(2):121-6.
Mycoplasma,
Chlamydia and Legionella are the usual organisms considered to be the
etiologic agents of 'atypical' pneumonia. Other microorganisms such as
bacteria, viruses, parasites, fungi and mycobacteria can also present
with atypical pneumonia manifestations. Outbreaks and isolated cases
of respiratory viruses with atypical pneumonia presentations have been
reported among immunocompetent and immunosuppressed patients. Severe
infections due to these respiratory viruses alone or as a concomitant
bacterial or viral infection have been observed. Additionally, in
endemic areas, certain zoonotic infections may present as atypical
pneumonia.
The role of atypical
pathogens: Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella
pneumophila in respiratory infection. Infect Dis Clin
North Am.1998 Sep;12(3):569-92, vii
Infections
caused by M. pneumoniae, C. pneumoniae, and Legionella spp. are
important causes of community-acquired pneumonia (CAP). In the past
decade, considerable new information has come to light concerning
these organisms. Despite this, debate continues concerning the
syndromic approach to CAP and the scientific merit of lumping these
pathogens together. Because the etiologic diagnosis of these pathogens
is established only in a minority of cases, the true prevalence tends
to be underestimated. In clinical practice, these pathogens are often
empirically treated. More rapid and cost-effective diagnostic
techniques are needed so that the clinical course of patients with
these infections can be better characterized.
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