Medical Resources :: Common Diseases :: Infectious Diseases & Parasites :: Latent Tuberculosis

Tuberculosis

• TB remains a major, global public health problem, particularly in developing countries
• Mycobacterium tuberculosis kills more people each year than any other single pathogen, according to the World Health Organization (WHO)
• In 1997, nearly 40% of new U.S. cases occurred in persons born in other countries

• Russia 4,491
• China 4,206
• Korea 1,829
• Guatemala 911
• Vietnam 603
• India 478
• Romania 406
• Total in 1998 15, 774 (INS data)

• Countries that children are adopted from abroad have high rates of tuberculosis
• Orphanage staff are paid low wages, live in crowded suboptimal housing, have inadequate nutrition and do not have access to health care
• Orphanage staff are at risk for TB disease

• Children living in orphanages have poor nutrition
• Undernutrition leads to immunosuppression and increases a child's susceptibility to infection
• Adults living, working, coughing in orphanages transmit TB to poorly nourished, immunosuppressed children

• Mantoux test contains 5 tuberculin units (TU) of purified protein derivative (PPD) and is administered intradermally and read at 48-72 hours by MD, RN, NP, PA
• Multiple puncture tests (MPTs) lack antigen standardization and are fraught with false-positive as well as false-negative results when compared to PPD

• Winthrop uses greater than or equal to 10 mm of induration as the cutoff for latent TB infection (LTBI)
• According to the Redbook 1997 this category is designed for children living in high-prevalence regions of the world
• 5 mm cutoff is used by a few experts

• PPD greater than or equal to 10 mm-chest film is recommended
• Normal chest x-ray-child is given a prescription for preventive therapy with isoniazid (INH) at a dose of 10 mg/kg given once daily by mouth for 9 months
• PPDs 6-9mm-possible chest film and a repeat PPD in 6-12 months

• Infants and young children with LTBI have been infected recently and are at higher risk of progression to actual disease
• Historic data suggest that untreated infants with LTBI have up to a 40% chance of developing tuberculosis disease and the risk decreases gradually through childhood
• Infants and young children are more likely than older children and adults to develop life-threatening forms of TB
• Isoniazid preventive treatment is more effective for children than adults (70-90%)
• Risk of INH hepatitis is very small in infants, children and adolescents (O'Brien et al. Pediatrics 1961; Stein et al. Pediatrics 1979)

• 286 children adopted from abroad tested for TB with PPD from July 1994 through August 1998 (China, Russia, EE, SE Asia, Latin America)
• All PPDs read by MD,RN, NP, or PA
• 193/286 (67.5%) 0 mm
• 31/286 (10.8%) 1-5 mm
• 12/286 (4.2%) 6-9 mm
• 17/286 (5.9%) 10-14 mm
• 33/286 (11.5%) greater than or equal to 15 mm
• 50/286 (17.5%) greater than or equal to 10 mm

• 103 children adopted from Russia tested for TB
• 56/103 (54.4%) 0 mm
• 12/103 (11.7%) 1-5mm
• 9/103 (8.7%) 6-9 mm
• 10/103 (9.7%) 10-14mm
• 16/103 (15.5%) greater than or equal to 15 mm
• 26/103 (25.2%) greater than or equal to 10 mm

• 139 children adopted from China tested for TB
• 111/139 (80%) 0 mm
• 14/139 (10.1%) 1-5 mm
• 3/139 (2.2%) 6-9 mm
• 5/139 (3.6%) 10-14 mm
• 6/139 (4.3%) greater than or equal to 15 mm
• 11/139 (8%) greater than or equal to 10 mm

• BCG is a live vaccine prepared from attenuated strains of M. bovis
• Used in more than 100 countries (not U.S.) primarily in young infants in an attempt to prevent disseminated TB, TB meningitis
• Various BCG vaccines used throughout the world differ in their make-up
• Vaccine efficacy of the different BCG vaccines appears to be highly variable (Redbook 1997)

• BCG vaccine is the most widely administered of all vaccines and has had little epidemiologic impact on TB
• An estimated 71% of infants worldwide born in 1989 received BCG (MMWR 1997)
• Randomized placebo-controlled clinical trials and retrospective case-control and cohort studies have demonstrated a wide variation in vaccine efficacy, ranging from 80% to zero!

• BCG confers protection against serious forms of childhood TB (miliary and meningitis) -80% efficacy (Redbook 1997)
• BCG may not prevent TB in the lung and other organs

• BCG vaccine is usually given within the first few days of life (Russia) or within the first few days of admission to an orphanage (China)
• BCG may be given multiple times
• BCG vaccine may be prepared improperly, stored inappropriately, administered ineffectively, or not administered at all
• Health records of BCG may be incomplete

• The scar is found on the upper right or left arm (occasionally children have scars on both upper arms, two scars on one arm)
• The scar may initially be red and weapy, then purple, dry and hard
• The scar may take weeks, months to heal
• The size of the scar varies
• The scar may be imperceptible
• Reports indicate that mean size of induration may be 3 mm to 18 mm (MMRW 1988; 37:663-4, 669-75)
• Studies indicate that TST induration attributed to BCG cross-reactivity decreases with increasing time since BCG administration (MMWR 1995;44, no. RR-11: 3-17)

• BCG efficacy does not correlate with postvaccination TST induration (MMWR 1988;37:663-4, 669-75)
• In other words, the TST size does not correlate with the quality of the BCG vaccine!

• On rare occasions (1-2%) the BCG vaccine results in a local adverse reaction
• A subcutaneous abscess accompanied by swelling of nodes in the axillary region (armpit) called "BCG itis" can occur
• Consultation with an infectious diseases consultant is recommended for management of such complications

• MMWR September 12, 1997 Botswana
• TSTs were administered and read for 783 children (median age 28 months)
• 73% of children had BCG scars
• Potency of PPD confirmed in Denmark
• 617 (79%) had zero reactivity after a TST, indicating that BCG did not result in TST induration

• RL Nemir & A Teichner. Management of tuberculin reactors in children and adolescents previously vaccinated with BCG. PIDJ 1983; 2: 446-451.
• M Lifschitz. The Value of the Tuberculin Skin Test as a Screening Test for Tuberculois among BCG-Vaccinated Children. Pediatrics 1965; 36: 624-627

• Winthrop China TB study-54% of children had BCG scars
• Winthrop Russia TB study-59% of children had BCG scars
• We are in the process of looking at the relationship of BCG to TST and it looks like there is no significant relationship-CDC TB Division Study 1997, 1998

• History of BCG is not a contraindication to skin testing
• Each case must be considered individually based on factors such as age, mm of induration, nutritional status, presence of BCG scar, record of BCG vaccination, country of origin, history of TB outbreak in orphanage in country of origin, opportunities for follow-up in the future.
  

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