Action needed on S. aureus in developing SE Asian countries

Medical Tribune March 2009 P12

David Brill

The burden of Staphylococcus aureus in low-income south and east Asian countries is poorly understood and could pose a threat to the health of both developed and developing countries, an international team of researchers has warned.

The lack of data on drug resistance rates in particular could exacerbate the problem if a strategic research program is not defined, the group wrote in a recent review in The Lancet Infectious Diseases. [2009 Feb;9(2):130-135]

The regional prevalence of methicillin-resistant S. aureus (MRSA), for example, remains largely unknown, although surveillance data from India and China suggest that the strain represents a substantial and rising proportion of the overall S. aureus burden. This knowledge gap could be contributing to the lack of recognition given to the problem by healthcare workers and the public, the study authors say.

The unregulated sale of cheap, substandard over-the-counter antibiotics could also be fuelling the emergence of MRSA in these countries, they add.

Mortality data on S. aureus in developing Asian countries are also scarce, but one study from a Thai hospital found that the death rate from bacteremia could be as high as 48 percent. [Lancet Infect Dis 2006 Feb;6(2):70-1] A comparable study in the US reported a mortality of just 22 percent. [Arch Intern Med 2003 Sep 22;163(17):2066-72]

Children seem particularly vulnerable to S. aureus in low-income countries in south and east Asia, unlike in high-income countries where the incidence of the bug appears largely to increase with age. The same study from Thailand found that S. aureus infections were most common in neonates, who made up 25 percent of all cases, while another study from Laos demonstrated that S. aureus was the number one cause of bacteremia in children aged under 1 year. [Am J Trop Med Hyg 2006 Nov;75(5):978-85]

“The burden of S. aureus disease in developing regions is inadequately appreciated or understood. An initiative is needed to raise the profile of S. aureus disease in developing countries, and to fund studies to better define the healthcare challenges and potential practical solutions relating to this important global pathogen,” wrote the authors, who hail from the Mahidol University in Bangkok, Thailand, the University of Oxford, UK, and the University of Washington in Seattle, US.

A total of 96 papers were included in the literature review – comprising published data from 20 low-income or lower-middle income countries including Indonesia, the Philippines, Vietnam and Cambodia.

Besides establishing the prevalence of MRSA, future research should also be directed at identifying risk factors for S. aureus and implementing cheap but effective mechanisms for infection control, the authors wrote.

Community-acquired MRSA: The new breed of nosocomial pathogen

Medical Tribune August 2008 P9
David Brill

The emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) as a nosocomial pathogen presents a range of new challenges for both prevention and management, according to a leading infectious disease specialist.

Professor Richard Wenzel, president of the International Society for Infectious Diseases, told the audience at the ICID that CA-MRSA appears to be more virulent than other nosocomial strains and has an unknown epidemiology.

He described the case that first “gave him respect for CA-MRSA:” a 22-year old male who deteriorated rapidly and died within 36 hours.

The patient had normal heart sounds on admission, yet developed a systolic murmur and symptoms of endocarditis after 16 hours. CT at presentation was also normal, yet MRI performed shortly before death showed around 100 brain abscesses which were later confirmed by biopsy.

It is unclear exactly what makes CA-MRSA so virulent, said Wenzel. The Panton-Valentine leucocidin (PVL) gene and alpha hemolysin have both been implicated in animal models, but their precise roles remain unclearly defined.

Screening also appears to be a complicated issue: a prospective cohort study of 51 CA-MRSA patients found that only 41 percent were nasal carriers, while a report of five patients who received the infection via heterosexual transmission revealed that only one was a nasal carrier.

Screening would therefore underestimate the prevalence of the USA-300 and USA-400 strains, Wenzel said, whereas in cases of nosocomial MRSA the majority of patients test positive for USA-100.

“This is important because people in the US are saying we just have to screen people so we know who’s out there. But it’s not that simple,” he said.

The antiobiogram for CA-MRSA also seems to differ from other types of infection, and the optimal treatment strategy remains unclear.

“The problem is what drugs do you use? I want to tell you this is getting complicated,” said Wenzel, who is chairman of the department of internal medicine at Virginia Commonwealth University, US.

“For life-threatening infections, antibiotics that inhibit protein synthesis and intravenous immunoglobulin may be useful,” he said, but noted that side effects are an issue with many of the available drug treatments.

“Linezolid we think is a relatively good drug but neuropathy, lactic acidosis and serotonin syndrome have all been described.

“Daptomycin looks good in comparative trials for skin and soft tissue. However, it’s not recommended for pneumonia because surfactant inhibits the antibacterial activity.”

He added that vancomycin can lead to renal failure when given with amino glycosides, while trimethoprim causes hyperkalemia in the majority of patients.

Definitive answers are still lacking on what treatments to use either for preventative prophylaxis of CA-MRSA or for treating ventilator-associated pneumonia, Wenzel said, noting that there are currently no clinical trials which can inform these decisions.

Improving our knowledge of resistant pathogens, drug interactions and the adverse events of antibiotics may help in future, he said.

“The plans for changing the prophylactic and empirical therapy for nosocomial infections need to begin right now,” he concluded.