Adult Long-Term Fever, Chills, Weight Loss

A 22-year-old male college student originally from India presents with fever, chills, night sweats, and weight loss of 4 weeks' duration. He received the Bacille–Calmette–Guérin (BCG) vaccine as a child. He moved to the United States 9 years ago.

He has no past medical history. He had an HIV test 3 months ago that was negative. His chest x-ray shows a right upper lobe infiltrate and mild hilar lymphadenopathy. No cavities are noted.

Sputum sample was taken with acid-fast Ziehl–Neelsen stain (see Figure).

What is the most likely organism?

• Legionella pneumophilia
• Mycobacterium tuberculosis
• Streptococcus pneumoniae
• Staphylococcus aureus

Key Facts about the BCG Vaccine:

• Usage:
  • The BCG vaccine is most widely used in countries where tuberculosis is common, such as parts of Africa, Asia, and Latin America.
  • It is routinely given to newborns and infants in high-risk countries to protect them from severe forms of tuberculosis, such as TB meningitis and miliary TB, both of which are more common in young children.
  • In countries with a low incidence of TB (e.g., the United States and most of Western Europe), the BCG vaccine is not routinely given due to low prevalence of the disease.
• Efficacy:
  • The BCG vaccine is particularly effective at preventing severe forms of TB in children, but its efficacy in preventing pulmonary TB (the most common and contagious form in adults) varies widely, with estimates ranging from 0% to 80% depending on the population and geographic location.
  • Protection against TB often diminishes with age, so it is generally not as effective for preventing adult TB.
• Mechanism of Action:
  • The BCG vaccine stimulates the immune system to recognize and fight Mycobacterium tuberculosis if exposed. It does not, however, protect against latent TB infection or reactivation of latent TB in most cases.
  • It also provides cross-protection against some other mycobacterial infections, like Mycobacterium leprae, the bacterium that causes leprosy.
• Administration:
  • The vaccine is given intradermally, usually in the upper arm.
  • A small, localized reaction typically develops at the injection site, which may ulcerate and leave a small scar. This is a normal part of the healing process and evidence of the vaccine's administration.
• Side Effects:
  • Common side effects include a small, localized ulcer or abscess at the injection site.
  • More serious side effects are rare but can include regional lymphadenitis (swelling of lymph nodes) or, in very rare cases, disseminated BCG infection, particularly in individuals with weakened immune systems.
    
    

This question appears in Med-Challenger Family Medicine Review with CME.