חיידקי שחפת מהירים

םיריהמ תפחש יקדייח

יוולו הרש ר"ד וכרעש םיריהמה תפחשה יקדייח לע רקחמה ריצקת
הדוגאה לש -35ה יתנשה סוניכב גצוהש ,היתימעו (Sara Valway)
.-14.9.97ב וקסיצנרפ-ןסב םייקתהש ,תוקבדימ תולחמל תינקירמאה

This was abstract #35 - presented at the 35th annual meeting of the
Infectious Disease Society of America in San francisco, Sept 14, 1997

Extensive Transmission of Mycobacterium
tuberculosis Due to Increased Virulence.

  S. VALWAY*, M. SANCHEZ, T. SHINNICK,
I. ORME, T. AGERTON, I. ONORATO.
CDC, Atlanta GA,  Colorado State University, CO, USA

From 1994-1996, a large community outbreak of tuberculosis (TB) occurred in a rural
area with a population about 10,000 and <1 TB case/year for the prior 10 years.
Twenty-one TB cases (15 culture positive) were identified; DNA fingerprints of the 13
available isolates are identical.To determine extent of transmission, investigation was
conducted among close and casual contacts of the cases. Virulence studies using mouse
models were also conducted on the outbreak strain of  M. tuberculosis.The Source Case,
diagnosed in 1994, Case B diagnosed in 1995, and Case C diagnosed in 1996 were the
sources of infection for the other 18 cases. Five secondary cases became infected and
developed active disease with only very limited, casual exposure to the Source Case, Case
B or Case C. Extensive transmission from these 3 cases to close and casual contacts was
also found; 337 (73%) of 461 contacts had positive TB skin tests and 86 had documented
skin test conversions. Mouse studies found that after 10 days, the virulent Erdman strain
of M. tuberculosis grew to 10³bacilli/lung, and after 20 days grew to about 10⁴
bacilli/lung.  In contrast, the outbreak strain grew to 2 x10⁶ bacilli/lung after 10 days and
about 10⁸ bacilli/lung after 20 days.  The extraordinary rate and extent of growth of the
outbreak strain of M. tuberculosis greatly exceeds that seen with other clinical isolates of
M. tuberculosis. These data  suggest increased transmission was a feature of the strain of
M. tuberculosis, eg, increased virulence, rather than an environmental factor or patient
characteristic.