C h a p t e r 2 2
Respiratory Tract Infections, Neoplasms, and Childhood Disorders
551
requires that a health care worker physically observe
the person’s ingestion of the medications, also improves
adherence to the program.
16
The primary drugs used are isoniazid (INH), etham-
butol, pyrazinamide, and rifampin. In addition to per-
sons with active tuberculosis, persons who have had
contact with cases of active tuberculosis and who are
at risk for development of an active form of the disease
are treated.
35–38
Prophylactic treatment is also used for
persons who have latent tuberculosis infection but do
not have active disease. These persons are considered to
harbor a small number of microorganisms and usually
are treated with INH.
34
Persons with drug-resistant
M. tuberculosis
infection
require careful supervision and more extensive drug
regimens.
36–38
Drug susceptibility tests are used to guide
treatment. Tuberculosis in persons with concomitant
HIV infection requires management by experts in both
tuberculosis and HIV.
Fungal Infections
Although most fungal infections are asymptomatic,
they can be severe or even fatal in persons who have
experienced a heavy exposure, have underlying immune
deficiencies, or develop progressive disease that is not
recognized or treated. The host’s cell-mediated immune
response is paramount in controlling such infections;
thus, immunocompromised persons, particularly those
with HIV infection, are particularly prone to develop-
ment of severe or fatal infection.
Pathologic fungi generally induce a delayed cell-medi-
ated hypersensitivity response to their chemical constit-
uents (see Chapter 15). Cellular immunity is mediated
by antigen-specific T lymphocytes and cytokine-acti-
vated macrophages that assume fungicidal properties.
The primary pulmonary lesions consist of aggregates
of macrophages stuffed with organisms, with similar
lesions developing in the lymph nodes that drain the
area. These lesions develop into granulomas complete
with giant cells and may develop central necrosis and
calcification resembling that of primary tuberculosis.
Types of Infections
Fungi are classified as yeasts and molds. Yeasts are
round and grow by budding. Molds form tubular struc-
tures called
hyphae
and grow by branching and form-
ing spores (see Chapter 14). Some fungi are
dimorphic,
meaning that they grow as yeasts at body temperatures
and as molds at room temperatures.
A simple classification of mycoses (diseases caused
by fungi) divides them into superficial, cutaneous, sub-
cutaneous, or deep (systemic) mycoses. The superficial,
cutaneous, or subcutaneous mycoses cause disease of
the skin, hair, and nails. Deep fungal infections may
produce pulmonary and systemic infections and are
sometimes fatal. They are caused by virulent fungi that
live freely, typically in soil or decaying organic matter
and frequently in specific geographic regions. The most
common of these are the dimorphic fungi,
Histoplasma
capsulatum
,
Coccidioides immitis
, and
Blastomyces
dermatitidis
.
39,40
These fungi form infectious spores,
which enter the body through the respiratory system.
Most people who become infected with these fungi
develop only minor symptoms or none at all—only a
small minority develop serious disease.
Each of the dimorphic fungi has a typical geographic
distribution.
H. capsulatum,
which is the etiologic agent
in
histoplasmosis
, is endemic along the major river val-
leys of the central and eastern United States (i.e., Ohio,
Missouri, Mississippi river valleys), eastern Canada,
Mexico, Central and South America, Africa, and south-
east Asia.
40,41
The organism grows in areas that have
been enriched with bird excreta: old chicken houses,
pigeon lofts, barns, and trees where birds roost. The
infection is acquired by inhaling the fungal spores that
are released when the dirt or dust from the infected areas
is disturbed.
C. immitis,
which causes
coccidioidomyco-
sis
, is most prevalent in the southwestern United States,
principally in California, Arizona, and Texas; Mexico;
and Central and South America.
40,42
Because of its prev-
alence in the San Joaquin Valley, the disease is some-
times referred to as
San Joaquin fever
or
valley fever.
C. immitis
lives in soil, and events that disturb soil, such
as dust storms and digging during construction, have
been associated with increased incidence of the disease.
B. capsulatum,
the agent causing
blastomycosis
, is most
commonly found in the south-central and northwestern
United States and Canada.
40,43
Clinical Features
Depending on the host’s resistance and immunocompe-
tence, the diseases usually take one of three forms: (1)
an acute primary disease, (2) a chronic (cavitary) pulmo-
nary disease, or (3) a disseminated infection. The lesions
of fungal infections consist of epithelioid cell granuloma-
tous containing aggregates of macrophages with engulfed
microorganisms. Similar nodules develop in the regional
lymph nodes. There is a striking similarity to the primary
lesions of tuberculosis. The clinical manifestations often
consist of a mild, self-limited flulike syndrome.
In the vulnerable host, chronic cavitary lesions
develop, with a predilection for the upper lobe of the
lung, resembling the secondary form of tuberculosis.
The most common manifestations are productive cough,
fever, night sweats, and weight loss. Disseminated dis-
ease most often develops as an acute and fulminating
infection in the very old or the very young or in per-
sons with compromised immune function. Although
the macrophages of the reticuloendothelial system can
remove the fungi from the bloodstream, they are unable
to destroy them. Characteristically, this form of the dis-
ease presents with a high fever, generalized lymph node
enlargement, hepatosplenomegaly, muscle wasting, ane-
mia, leukopenia, and thrombocytopenia. There may be
hoarseness, ulcerations of the mouth and tongue, nausea,
vomiting, diarrhea, and abdominal pain. Often, menin-
gitis becomes a dominant feature of the disease. Persons
with blastomycosis may experience cutaneous infections
