CONFERENCE NEWS UPDATE
39th INTERSCIENCE CONFERENCE ON ANTIMICROBIAL AGENTS AND CHEMOTHERAPY

SAN FRANCISCO-Among the flurry of studies presented at the recent 39th Interscience Conference on Antimicrobial Agents and Chemotherapy in San Francisco were reports about fluoroquinolone resistance in gram-negative bacteria and the fact that Staphylococcus aureus is on the rise in Asia and South Africa. In addition, researchers noted that the occurrence of antimicrobial resistance among food animals can be reduced by limiting the use of antibiotics.

An investigational vaccine has shown efficacy in preventing pneumonia in children, especially the severe cases, according to findings presented by Steven Black, MD, and Henry Shinefield, MD, who are Co-Directors of the Kaiser Permanente Vaccine Study Center in Oakland, Calif.

The 3-year trial involved 37,000 children who were randomly assigned to a heptavalent pneumococcal conjugate or to a control vaccine. Each child was given doses at 2, 4, 6, and 12 to 15 months.

The investigational vaccine was associated with a 73.1% reduction in cases of severe pneumonia, as confirmed by a radiograph showing a large area of pneumonia infection, and a 33% reduction in pneumonia, as confirmed by a radiograph showing some pneumonia infection. In addition, children who received the investigational vaccine had an 11.4% reduction in physician visits due to pneumonia compared with children who received the control drug. The vaccine was also effective in reducing the incidence of otitis media and the need for pressure equalization tube placement.

"We have extensively evaluated the vaccine's safety and efficacy in a large population over a long period of time," said Dr. Shinefield. "I think parents and physicians will welcome this vaccine because it will be effective in fighting a threat to the health of young children."

Nose blowing can transmit nasal bacteria and viruses into the sinuses, according to a study conducted by Jack M. Gwaltney, Jr, MD, of the University of Virginia School of Medicine in Charlottesville, and colleagues. The findings provide new insight into the mechanisms by which sinusitis occurs and have implications for the treatment of colds.

Intranasal pressure was measured during coughing, sneezing, and nose blowing in four healthy adult volunteers. Then, radiopaque contrast medium was placed in the noses of 10 healthy adult volunteers and computed tomography (CT) was used to determine whether the contrast material was deposited into the sinuses after the patients coughed, sneezed, or blew their noses.

Coughing and sneezing produced a much lower pressure in the nose compared with nose blowing (mean maximal intranasal pressure, 4.6, 6.6, and 66 mmHg, respectively). The CT studies showed that sneezing and coughing did not propel the contrast medium into the sinuses. However, the contrast medium was found in at least one sinus of all four subjects who blew their noses. A simple fluid model indicated that a single nose blow can propel up to 1 mL of mucus from the middle meatus into the maxillary sinus, the researchers reported.

Thus, treatments that reduce nasal fluid production are desirable not only for their symptomatic benefits but also because of the possibility that they may help prevent spreading the cold to the sinuses, the researchers noted.

Data collected from the SENTRY Antimicrobial Surveillance Program for 1998 show that significant levels of fluoroquinolone resistance in gram-negative bacteria and Staphylococcus aureus are now being seen in Asia and South Africa.

John Turnidge, MD, and colleagues from the Women's and Children's Hospital, North Adelaide, Australia, designed the study to examine fluoroquinolone resistance in their region. The program covers 16 hospital laboratories in Australia, Hong Kong, Japan, Mainland China, the Philippines, Singapore, South Africa, and Taiwan. Blood culture, fastidious respiratory, lower respiratory, skin/skin structure, and urinary isolates were tested against a range of fluoroquinolones, including ciprofloxacin, trovafloxacin, grepafloxacin, gatifloxacin, and levofloxacin. The incidence of resistance to ciprofloxacin is shown in the Table.

"In general, results for these pathogens with the newer quinolones correlated with ciprofloxacin," the researchers explained.

Resistance to grepafloxacin/trovafloxacin was found in one of the 221 Streptococcus pneumoniae isolates tested. There were no cases of resistance to Haemophilus influenzae.

A new study from Denmark suggested that it is possible to reduce the occurrence of antimicrobial resistance among food animals by removing or limiting the use of antibiotics. The study was conducted by Frank M. Aarestrup, MD, and colleagues from the Danish Veterinary Laboratory in Copenhagen, Denmark.

Major changes in the use of antimicrobial agents for growth promotion have occurred in Denmark since 1995, the researchers explained. For example, the use of avoparcin was banned in 1995 because of the development of vancomycin-resistant enterococci and the potential spread of this resistance through the food chain to humans. In addition, virginiamycin was banned in 1998 because of cross-resistance to quinupristin-dalfopristin, which is a streptogramin used to treat humans.

The Danish Integrated Antimicrobial Resistance Monitoring Programme was established in 1995 to determine the occurrence of resistance to antimicrobials among different food animals in Denmark. Under this program, bacteria are continuously isolated from broilers, cattle, and pigs and tested for susceptibility to antimicrobials used for therapy or growth promotion.

The researchers noted a decrease in the incidence of resistance to glycopeptides and avilamycin among Enterococcus faecium from broilers following decreased use of these agents. Resistance to virginiamycin among E faecium from pigs and broilers increased between 1995 and 1997 due to increased consumption of this agent but decreased after the ban of this agent in 1998. Furthermore, resistance to the macrolide tylosin apparently decreased among enterococci from pigs during 1998 when use of that agent was limited.

In contrast, resistance to quinolones among Escherichia coli, Salmonella enterica, and Campylobacter coli increased among pigs and cattle, possibly because of an increased use of the fluoroquinolone enrofloxacin. There was also an increase in the occurrence of resistance to streptomycin and tetracycline among E coli isolated from healthy pigs and the occurrence of streptomycin resistance among Salmonella enterica and E coli isolated from cattle. In addition, a high level of resistance to several commonly used antibiotics was found for pathogenic E coli isolated from infections in the animals.

The incidence of penicillin-resistant Streptococcus pneumoniae (PRSP) infection increased dramatically from 1995 to 1997 in the Baltimore metropolitan area, according to findings reported by Bernadette Albanese, MD, of Johns Hopkins University in Baltimore and colleagues. Children younger than age 5 years, the elderly, and urban dwellers were at highest risk for PRSP, suggesting that control efforts should be targeted toward these groups.

The findings are based on data from the Maryland Emerging Infections Program, which uses laboratory-based surveillance to track diseases. Data on minimum inhibitory concentrations (MICs) were available for 1,693 of the 2,094 cases of invasive pneumococcal disease that were found from 1995 to 1997. These data showed that 7.4% of the overall cases were caused by PRSP and that this incidence increased 42% (from 5.7% to 8.1% of cases) during the study period.

The PRSP rate (the number of PRSP cases per 100,000) was significantly higher for children younger than age 5 years (4.3) and people age 65 years and older (4.1) compared with other age-groups (1.1%; P<.01). Overall, whites had a higher incidence compared with blacks (9.7% vs 5.2%); however, in the age-group of 20 to 44 years, the incidence was increased 5.7-fold among blacks compared with whites (P=.01). While a significantly higher proportion of cases from suburban counties were caused by PRSP compared with urban counties (10% vs 6%; P<.001), the rate of PRSP was greater in urban counties than in suburban counties (2.8 vs 1.3; P=.02).

Furthermore, a higher proportion of cases occurred from November to April compared with that during the period of May to October (8.4% vs 5.4%; P=.03), and this difference was particularly marked among people age 65 years and older (10.3% vs 1.4%; P<.001). "The seasonality of PRSP suggests that recent antibiotic use, which is more common in winter months, may rapidly affect the prevalence of resistant pneumococcal infections," the researchers noted.

-Kristin Della Volpe

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