Literature Update - July, 2004
Compiled by Dr Deb Friedman, VICNISS ID Physician
Short-Course Rifampicin and Pyrazinamide Compared with Isoniazid for Latent Tuberculosis Infection
Several years ago, clinicians began using a combination of rifampicin and pyrazinamide to treat patients with latent
tuberculosis, instead of using isoniazid. However, a recent study (Jasmer RM et al, Clin Infect Dis 2004) adds to the
growing body of evidence that 2 months of rifampicin and pyrazinamide (2RZ) is both more toxic and less cost-effective
than the standard of 6 months of isoniazid treatment for latent tuberculosis infection (LTBI).
The clinical trial found that 2RZ was associated with a statistically significant higher risk of hepatotoxicity than
was 6 months of treatment with isoniazid, resulting in discontinuation of rifampin and pyrazinamide (RZ) treatment.
The Centers for Disease Control and Prevention (CDC), in conjunction with the American Thoracic Society and the
Infectious Disease Society of America now recommend against the use of rifampicin and pyrazinamide, and it should
generally not be offered to either HIV-negative or HIV-infected persons with LTBI.
Nosocomial Pneumonia in ICU
A Brazilian hospital has published their experience with hospital-acquired pneumonia in ICU, and attempted to estimate
the duration of time between admission and disease onset (Enoy Neves Gusmão M, Am J Infect Control 2004;32:209-15).
They found that it took an average of 85 hours for patients to develop nosocomial pneumonia, and that important risk
factors included age greater than 50 years, mechanical ventilation, and antibiotic use.
Coagulase-Negative Staphylococcus in Blood Cultures-True BSI or Contaminant?
It is very difficult for both clinicians and infection control staff to figure out if a blood culture which grows
Coagulase-negative Staphylococcus (CNS) represents a true bloodstream infection or merely contamination.
A researcher from the CDC has constructed a mathematical model of blood cultures positive for CNS in patients with
central lines to assist with this process (Tokars J, Clin Infect Dis 2004;39:000).
Although it is a complicated read, the upshot is that 2 or more positive blood cultures for CNS are highly predictive
of a true BSI, while single positive blood cultures carry a relatively low positive predictive value. This type of model
may well influence future changes to the definitions of catheter-associated BSI that both we, and other countries utilise.
The Role of the Intestinal Tract as a Reservoir and Source for Transmission of Nosocomial Pathogens
A recent review article, improves our understanding about nosocomial pathogens which arise from the intestinal tract
(Donskey CJ, Clin Infect Dis 2004;39:219-226).
There are many important factors which play a role in this process (see Figure below). Host factors such as reduced gastric
acidity, in conjunction with illness, antibiotics and invasive devices and finally diarrhoea or incontinence all assist in
transmitting such pathogens within the hospital.
The author also describes several control measures that may limit transmission of multiple pathogens. These include:
- "Selective" decontamination of the intestinal tract (to selectively inhibit pathogens in the gastrointestinal tract
without disturbing the anaerobic microflora)
- Antibiotic restriction strategies (for example; preventing initiation of unnecessary therapy, and by shortening
antibiotic courses)
- Maintenance of stomach acidity (by avoiding acid-blocking medication)
- Preservation or restoration of the indigenous colonic microflora (for example by administration of probiotics)
- Decontamination of environmental surfaces or patients' skin (for example by using a chlorhexidene gluconate body cleanser)