_Mycobacterium nonchromogenicum_ Bacteremia in an AIDS Patient

To the Editor: _Mycobacterium avium_ complex is the most common
nontuberculous mycobacterium that causes disseminated infection in
HIV-positive patients (1). Other less common nontuberculous mycobacteria
responsible for disseminated disease in these patients are _M. fortuitum_
(2), _M. genavense_ (3), _M. gordonae_ (4),_ M. haemophilum_ (5), _M.
kansasii_ (6), _M. malmoense_ (7), _M. marinum_ (8), _M. scrofulaceum_ (9),
_M. simiae_ (10), _M. szulgai_ (11), _M. terrae_ (9), and _M. xenopi_
(2,9). Although only _M. genavense_, _M. kansasii_, and _M. xenopi _are
significantly more frequent in these patients (2,3,9), HIV infection is
likely a predisposing condition for all nontuberculous mycobacterial
infections. We report the first case of disseminated infection caused by
_M. nonchromogenicum_ in an HIV-infected patient.

A 28-year-old man with HIV infection acquired by sharing injection tools
was seen in our outpatient clinic because of intermittent fever, drenching
nocturnal sweats, and cough with purulent sputum of 4 months' duration. He
also reported a weight loss of 10 kg in the previous 2 months. He had been
treated for bronchial infection with an unknown antibiotic in another
hospital. After this treatment, respiratory symptoms had improved somewhat,
but fever and constitutional symptoms continued. His only previous
opportunistic infection had been recurrent oral and esophageal candidiasis.
The last CD4-cell count had been 16/µL 1 year earlier, and he was receiving
didanosine and prophylactic therapy with cotrimoxazole and fluconazole. On
physical examination the patient appeared ill; he was febrile, cachectic,
and had thrush and oral hairy leukoplakia. Neither lymphadenopathy nor
abnormal cardiopulmonary symptoms were found. The liver, which had enlarged
since the last examination, was palpated 6 cm below the right costal
margin. Abnormal laboratory values included aspartate aminotransferase 61
U/L, gamma-glutamyl transferase 209 U/L, lactate dehydrogenase 516 U/L,
hemoglobin 12.3 g/dL, leukocyte count 4,300/µL (66% neutrophils, 19% band
forms, 1% metamyelocytes, 3% lymphocytes, 11% monocytes), platelet count
130,000/L, and erythrocyte sedimentation rate 72 mm/h. Chest X-rays were
unremarkable, and a set of blood cultures was sterile. A sputum culture
yielded _Haemophilus influenzae_ sensitive to ampicillin, and smears and
cultures for mycobacteria in one stool and three sputum samples were
negative.

The patient was treated with oral amoxicillin for 2 weeks without
improvement. Empirical therapy against _M. avium_ complex with
clarithromycin, ciprofloxacin, and ethambutol was started; the patient's
condition improved dramatically within the next few days, and the fever and
diaphoresis disappeared, although cough and sputum production remained
unchanged. Three weeks later, a slow-growing nonphotochromogenic
mycobacterium, identified as _M. nonchromogenicum_ in a reference
laboratory (Centro Nacional de Microbiología, Majadahonda, Madrid, Spain)
by biochemical tests and confirmed by polymerase chain reaction-restriction
enzyme pattern analysis, was isolated from a blood sample obtained on
admission. This microorganism was sensitive to the three drugs
administered, and the treatment was continued. Two months later the patient
had gained 10 kg, hemoglobin had increased to 13.8 g/dL, the erythrocyte
sedimentation rate had decreased to 52 mm/h, and the differential leukocyte
count had returned to normal. Antimycobacterial drugs were withheld after 1
year of treatment. Twenty-two months after the diagnosis, the patient is
doing well. He is receiving combination antiretroviral therapy, and his
CD4-cell count is 128/µL.

_M. nonchromogenicum_, a slow-growing nonpigmented (Runyon's group III)
mycobacterium, belongs to the _M. terrae_ complex, together with _M.
triviale_; it is traditionally considered nonpathogenic. However, it has
been involved in a few cases of pulmonary infection (12) and chronic
tenosynovitis secondary to puncture wounds (13), like the related organism
_M. terrae_. In fact, some authors think that _M. nonchromogenicum_ is the
true pathogen in the _M. terrae_ complex (13), and it is possible that some
reports have misidentified this organism. This complex was first isolated
in soil washings from radishes, but it has been found to be ubiquitous in
the aquatic environment, including a hospital potable water supply (14).

Unlike osteoarticular infections, which commonly occur in previously
healthy people, the scanty reports on pulmonary and disseminated infection
by _M. terrae_ complex suggest that either immunosuppression or local
predisposing conditions (e.g., tuberculous cavities) are necessary
pathogenetic cofactors (15). To our knowledge, _M. nonchromogenicum_
bacteremia has never been reported before.

No specific DNA probes exist for _M. terrae_ complex, but false-positive
reactions with _M. tuberculosis_ complex DNA probes have been described
(16). Isolates are usually resistant to most antituberculosis drugs, with
the exception of ethambutol and streptomycin, and susceptible to
erythromycin, ciprofloxacin, and sulfonamides.

Only one case of disseminated infection by _M. terrae_ has been described
in a patient with advanced HIV infection and positive cultures in blood and
bronchoalveolar lavage fluid, but no additional data were provided (9).
Although the isolate we recovered might represent a laboratory contaminant,
several pieces of evidence make this possibility very unlikely: lack of
alternative explanation for a persistent and progressive clinical picture
of 4 months' duration, absence of response to standard antibiotic therapy,
negative results in the search for other pathogens, rapid and sustained
clinical and laboratory response to drugs active against this strain, clear
improvement despite the lack of treatment for other conditions, and absence
of other isolates of this pathogen in our hospital despite the large number
of samples examined for mycobacteria.

Acknowledgments

We are indebted to María Soledad Jiménez, Mycobacterial Laboratory of the
Centro Nacional de Microbiología, Majadahonda, Madrid, for providing the
microbiologic data.

José Mayo, Julio Collazos, and Eduardo Martínez
Hospital de Galdakao, Vizcaya, Spain

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