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WASHINGTON, D.C. -- Re-emerging infectious diseases pose a serious threat to the nation's public health. Today, experts addressed key developments to the current and future outlook of infectious diseases, including the evolving adult immunization platform and also highlighting recent outbreaks of polio, mumps and pertussis, Clostridium difficile, and community-associated methicillin-resistant Staphylococcus aureus, at a news conference sponsored by the National Foundation forInfectious Diseases (NFID).
Outbreaks of Polio, Mumps, and Pertussis: Childhood Scourges Come Back to Haunt Us
Vaccine development and routine childhood immunization present one of the most tangible contributions to the public's health. For each birth cohort receiving routine childhood vaccines (targeting 10 diseases), there are an estimated 33,000 lives saved, 14 million infections prevented, and $10 billion in healthcare savings. Immunization coverage is at the highest level ever recorded, and the number of diseases targeted for prevention through routinely recommended childhood vaccines increased from seven in 1985 to 15 as of early 2006. Most vaccine-preventable diseases are at an all-time low. Yet outbreaks of forgotten diseases -- including mumps, whooping cough (pertussis), and on the international front, paralytic polio, are being reported.
"There are multiple factors contributing to these outbreaks," stated Anne Schuchat, MD, director of the NationalCenter for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention (CDC). In contrast to the measles resurgence of 1989 - 1991, which was caused by low immunization coverage of preschool-aged children, the spotlight for increases in pertussis and mumps in the United States shines on adolescent or adult populations. The increase in pertussis is attributed to important reservoirs for infection in adolescents and adults whose immunity waned since childhood vaccination. "The licensure in 2005 of new booster vaccines (Tetanus-diphtheria-accellular pertussis or Tdap) appropriate for these age groups provides an optimistic outlook for achieving improved control of pertussis," said Schuchat.
Schuchat also discussed the recent outbreaks of mumps in college students in the Midwestern United States and the United Kingdom and polio transmission in Nigeria, where large unvaccinated populations permitted resurgent diseases that spawned outbreaks in numerous other previously polio-free countries.
"These three vaccine-preventable disease resurges illustrate that low immunization coverage, waning immunity, and accumulation of susceptibles can each provide challenges to disease control. New vaccines and innovative immunization strategies can reverse these trends. Yet we can never become complacent to returns in vaccine-preventable diseases, but must maintain strong programs and public confidence in vaccines and our immunization system," Schuchat added.
Re-emergence of an Old Foe:Â Clostridium difficile
Clostridium difficile is a gram positive, spore-forming organism that has been recognized as a major nosocomial pathogen worldwide. Infection occurs exclusively in the colon. C. difficile causes a spectrum of disease from diarrhea to toxic megacolon (inflammation of the colon) that may require colectomy (surgical removal of the colon) and can lead to death. Clostridium difficile appears to be one of several pathogens that is re-emerging with increased virulence and is challenging scientists to explain its incidence, virulence, and the epidemiology. "The re-emergence of this pathogen, that occurs almost exclusively in the presence of antibiotic exposure provide challenges to clinicians who treat patients with the infection and infection control personnel who prevent its spread," said Trish M. Perl, MD, Msc, associate professor in the departments of medicine (Infectious Diseases) and pathology at JohnsHopkins University School of Medicine and in the department of epidemiology at the Bloomberg School of Hygiene at JohnsHopkinsUniversity. Perl is also director of hospital epidemiology and infection control, and hospital epidemiologist at JohnsHopkinsHospital.
Prevention and control of Clostridium difficile has been difficult in healthcare settings. Several specific characteristics of the organism explain the challenges for prevention and control. First, the organism contaminates the environment. Second, because it is a spore-forming organism, it is likely to be relatively resistant to chemical disinfectants. Third, limited resources in hospitals and shared equipment that has not or cannot be cleaned lead to cross contamination. Fourth, the antimicrobial resistance that is reportedly increasing may contribute to the organism's emergence in high-risk patients. Finally, in addition to cross transmission, antimicrobial use is a risk factor for disease. Multiple studies suggest that in addition to traditional infection control measures, antimicrobial stewardship and formulary manipulation are needed to control disease.
"Control likely hinges on prevention and enhanced efforts to interrupt disease transmission. Physicians and infection control professionals need to be alert to the possibility of an increasing incidence and perhaps epidemics of unusually serious cases. Prevention strategies include disease recognition, the fastidious use of barrier precautions, patient isolation, careful cleaning of the environment with sporocidal agents active against C. difficile, use of soap instead of alcohol-based skin cleansing and, perhaps most important, antibiotic stewardship," stated Perl.
Community-Associated Methicillin-Resistant Staphylococcus aureus and Its Impact on Hospitals
Since the 1980s, the bacterium, methicillin-resistant Staphylococcus aureus, or MRSA, has been synonymous with the hospital-associated infections (HAIs). A new kind of MRSA emerged in the late 1990s from the community (CA). CA-MRSA is genetically different from HA-MRSA and though resistant to one antibiotic, methicillin, CA-MRSA's growth is inhibited by several other antibiotics. "The new community acquired MRSA affect a new population: Healthy children and adults who have none of the risk factors typically found in persons with HA-MRSA infections like hospitalization, exposure to a healthcare workers, surgery, residence in a chronic care facility or exposure to a dialysis unit," said Carol J. Baker, MD, professor of pediatrics, molecular virology and microbiology, and head of the infectious diseases section at Baylor College of Medicine and president of NFID.
Typically, CA-MRSA infections involve the skin and soft tissues. One clue to CA-MRSA infections is that other family members have or have had similar infections in the past few months. Outbreaks have been reported in competitive sports participants, usually contact sports, military recruits, and day care attendees. Factors common to these settings that facilitate the spread of CA-MRSA are crowding, skin-to-skin contact, participation in activities that result in compromised skin surfaces, sharing of personal items that can become contaminated with wound drainage such as towels, poor personal cleanliness and hygiene, and limited access to healthcare. Outbreaks in professional football teams have reached the headlines in the past two years. However, while outbreaks are rare, most children and adults with CA-MRSA are not part of an outbreak.
"The key to preventing CA-MRSA infections is hygiene and avoidance of skin trauma. Antibiotic treatment and drainage can cure most CA-MRSA infections, but antibiotics don't rid the nose, throat, gastrointestinal tract or skin of CA-MRSA. There are no vaccines and antibacterial ointments do not work," explained Baker.
The Evolving Adult Immunization Platform
The traditional focus of immunization activities has been on infants, children and adolescents. This immunization effort has been extraordinarily successful in virtually eliminating many diseases, as well as racial and socioeconomic disparities. Several vaccines recently licensed are targeted to adults, including those for Tetanus-diphtheria-accellular pertussis (Tdap), Human Papillomavirus (HPV), and Herpes zoster (shingles). William Schaffner, MD, professor and chair of the department of preventive medicine, division of infectious diseases at VanderbiltUniversity School of Medicine presented updates on these new vaccines.
Schaffner outlined the challenges in implementing vaccines in the adult population. "Financing vaccines and their administration, educating the public and providers about the vaccines and their benefits, and creating a public health and private medicine infrastructure to deliver the vaccines remain challenges to optimal implementation of these and future vaccines for adults," said Schaffner.
Source: National Foundation for Infectious Diseases