Recent and rapid emergence of W-Beijing strains of Mycobacterium tuberculosis in Cape Town, South Africa.

BACKGROUND: There is increasing evidence of a strain-related variation in the virulence in Mycobacterium tuberculosis that may afford a selective advantage to certain strains. The W-Beijing strain family is globally distributed, highly virulent in animal models, associated with human immunodeficiency virus infection and drug resistance, and may be an emerging strain family. Our goal was to determine whether W-Beijing strains are expanding in a region of South Africa where rates of tuberculosis are among the highest in the world. METHODS: We used spoligotyping and single nucleotide polymorphism analysis to genotype all strains of tuberculosis from children presenting to the major pediatric referral hospital in Cape Town, South Africa over a period of 4 years and strains present in 352 archived histological samples from over a 76-year period. RESULTS: The proportion of W-Beijing strains from children increased from 13% to 33% from 2000 to 2003 (P= .026). With regard to the histological samples, W-Beijing strains were absent in the samples from the period 1930-1965 and rare in the samples from the period 1966-1995 (2.8% of samples), but they were increasingly common in samples from the period 1996-2005 (20% of samples; P= .001). CONCLUSIONS: The rapid expansion of W-Beijing strains in a region with a very high background incidence of tuberculosis suggests that these strains have a significant selective advantage. The biological reasons for this observation remain unclear but warrant further study. The rapid spread of this virulent strain lineage is likely to present additional challenges for tuberculosis control.

How reliable is a negative blood culture result? Volume of blood submitted for culture in routine practice in a children's hospital.

OBJECTIVES: The primary aims of this study were to determine the volume of blood submitted for culture in routine clinical practice and to establish the proportion of blood cultures with a blood volume inadequate for reliable detection of bacteremia. METHODS: The volumes of blood samples submitted for culture from infants and children up to 18 years of age were measured over a 6-month period. Blood cultures were deemed adequate submissions if they contained an appropriate (age-related) volume of blood and were submitted in the correct blood culture bottle type. During the study, an educational intervention designed to increase the proportion of adequate blood culture submissions was undertaken. RESULTS: The volume of blood submitted in 1358 blood culture bottles from 783 patients was analyzed. Of the 1067 preintervention blood cultures, 491 (46.0%) contained an adequate blood volume and only 378 (35.4%) were adequate submissions on the basis of collection into the correct blood culture bottle type. After the intervention, there were significant increases in both the proportion of blood cultures containing an adequate blood volume (186 [63.9%] of 291 cultures) and the proportion of adequate submissions (149 [51.2%] of 291 cultures). Overall, blood cultures with an adequate blood volume were more likely than those with an inadequate blood volume to yield positive blood culture results (34 [5.2%] of 655 cultures vs 14 [2.1%] of 648 cultures). Similarly, adequate blood culture submissions were more likely than inadequate submissions to yield positive blood culture results (26 [5.1%] of 506 cultures vs 22 [2.8%] of 797 cultures). CONCLUSIONS: In routine clinical practice, a negative blood culture result is almost inevitable for a large proportion of blood cultures because of the submission of an inadequate volume of blood. Even after an educational intervention, nearly one half of blood cultures were inadequate submissions.