How does mycobacteriemia (presence of mycobacteria in the blood) typically present?

Clinical Presentation of Mycobacteriemia

Mycobacteriemia (disseminated nontuberculous mycobacterial infection) presents most characteristically with fever (80%), night sweats (35%), and weight loss (25%), occurring almost exclusively in severely immunocompromised patients with CD4 counts <50 cells/µL. 1

Patient Population and Risk Factors

The clinical presentation depends critically on the immune status of the host:

HIV/AIDS Patients (Most Common)

• Disseminated disease occurs almost exclusively when CD4 count falls below 50 cells/µL, with average CD4 counts at presentation typically <25 cells/µL 1
• In the pre-antiretroviral era, nearly 40% of patients with <10 CD4 cells/µL developed disseminated NTM within one year 1
• Mycobacterium avium complex (MAC) accounts for the vast majority of cases in this population 1

Non-HIV Immunocompromised Patients (Rare)

• Disseminated NTM is very rare outside of advanced HIV disease 1
• When it occurs, it is typically in patients with renal or cardiac transplantation, chronic corticosteroid use, or leukemia 1
• In non-AIDS patients, MAC typically presents as fever of unknown origin 1
• Rapidly growing mycobacteria (M. chelonae, M. abscessus) present as multiple subcutaneous nodules or abscesses that may spontaneously drain 1

Constitutional Symptoms

The classic triad dominates the clinical picture:

• Fever: Present in 80% of patients with disseminated MAC 1
• Night sweats: Occur in 35% of cases 1
• Weight loss: Affects 25% of patients 1

These symptoms typically develop over 1-2 months before bacteremia becomes detectable 1

Gastrointestinal Manifestations

• Abdominal pain and diarrhea are common presenting complaints 1
• Abdominal tenderness may be present on examination 1
• Hepatosplenomegaly can occur, though palpable lymphadenopathy is uncommon 1

Laboratory Abnormalities

Key laboratory findings include:

• Severe anemia with hematocrit <25% 1
• Elevated alkaline phosphatase 1
• Elevated lactate dehydrogenase 1

These abnormalities typically appear 1-2 months before onset of bacteremia 1

Organ Involvement Patterns

Pulmonary Disease (Uncommon in Disseminated Disease)

• Clinical lung involvement is rare in AIDS patients with disseminated MAC, occurring in only 2.5% of cases 1
• Autopsy studies show widespread internal organ involvement even without localizing symptoms 1
• Finding MAC in respiratory samples should prompt investigation for disseminated disease, as approximately 10% of patients with CD4 <50 cells/µL have MAC isolated from sputum, and many eventually develop dissemination 1

Lymphadenopathy

• Peripheral lymphadenopathy is not common in typical disseminated MAC 1
• When present, excision and culture of accessible nodes may be needed for diagnosis if blood cultures are negative 1

Immune Reconstitution Inflammatory Syndrome (IRIS)

Patients initiating antiretroviral therapy may develop a paradoxical worsening:

• Suppurative lymphadenopathy with swollen, painful cervical, axillary, or inguinal nodes is the most common IRIS manifestation 1
• Other presentations include pulmonary infiltrates, soft tissue abscesses, or skin lesions 1
• Fever is frequent but other components of MAC bacteremia syndrome are typically absent 1

Diagnostic Approach

Blood cultures are the cornerstone of diagnosis:

• Over 90% of patients with disseminated MAC have positive blood cultures 1
• One positive blood culture is sufficient for diagnosis 1
• Blood cultures should be performed in symptomatic patients with compatible clinical features 1
• Routine screening blood cultures in asymptomatic patients are not recommended, even with CD4 <100 cells/µL 1

Alternative diagnostic methods when blood cultures are negative:

• Bone marrow or liver biopsy and culture may be indicated after two negative blood cultures in symptomatic patients 1
• Fine needle aspiration of intrathoracic, intraabdominal, or retroperitoneal adenopathy may be required 1

Important Clinical Pitfalls

• Do not confuse with tuberculosis: The clinical presentation can mimic numerous other infections, making diagnosis challenging 1
• Respiratory isolation of MAC does not equal pulmonary disease: In HIV patients, MAC in sputum usually represents colonization or early dissemination rather than active lung disease 1
• Species variation matters: M. intracellulare causes most MAC lung disease, but M. avium causes most disseminated disease in AIDS 1
• Physical examination is often nonspecific: The absence of localizing findings does not exclude widespread organ involvement 1