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Prevention of Infectious Diseases

Much of the decline in the incidence and fatality rates of infectious diseases is attributable to public health measures—especially immunization, improved sanitation, and better nutrition.

Immunization remains the best means of preventing many infectious diseases. In the United States, childhood immunization has resulted in near elimination of measles, mumps, rubella, poliomyelitis, diphtheria, pertussis, and tetanus. Haemophilus influenzae type b invasive disease has been reduced by more than 95% since the introduction of the first conjugate vaccines. However, substantial vaccine-preventable morbidity and mortality continue to occur among adults from vaccine-preventable diseases such as hepatitis A, hepatitis B, influenza, and pneumococcal infections. For example, in adults in the United States, there are an estimated 50,000–70,000 deaths annually from influenza, hepatitis B, and invasive pneumococcal disease. Yet in 2002, only about 65% of elderly persons reported receiving influenza and pneumococcal vaccines. The American College of Physicians recommends that clinicians should review each adult's immunization status at age 50; assess risk factors that would indicate a need for pneumococcal vaccination and annual influenza immunizations; reimmunize at age 65 those who received an immunization against pneumococcus more than 6 years before; ensure that all adults have completed a primary diphtheria-tetanus immunization series, and administer a single booster at age 50; and assess the postvaccination serologic response to hepatitis B vaccination in all recipients who have ongoing risks of exposure to blood or body fluids (eg, sharp injuries, blood splashes).

Recently, strategies have also been proposed to improve influenza, pneumococcal polysaccharide, and hepatitis B targeted vaccination; in other words, improve coverage among those adults aged 65 years or younger who are at high risk for exposure or disease. Strategies to enhance vaccinations in general include increasing community demand for vaccinations; enhancing access to vaccination services; and provider- or system-based interventions, such as reminder systems. Clinicians can substantially improve immunization rates by use of standing orders and algorithms, expanded nurse decision-making, patient education and incentives, and partnership with community pharmacies. Increasing reports of pertussis among US adolescents, adults, and their infant contacts have stimulated vaccine development for older age groups. A safe and effective tetanus-diphtheria 5-component acellular pertussis vaccine (Tdap) is now available for use in adolescents and adults. On October 26, 2005, the Advisory Committee on Immunization Practices (ACIP) recommended routine use of a single dose of Tdap for adults aged 19–64 years to replace the next booster dose of tetanus and diphtheria toxoids vaccine (Td). The ACIP also recommended Tdap for adults who have close contact with infants younger than 12 months, for pregnant women, and women who are planning a pregnancy.

In 2002, the ACIP approved a schedule for the routine vaccination of persons aged 19 years and older. Recommended immunization schedules for children and adolescent are set forth in Table 30–4. Persons traveling to countries where infections are endemic should take precautions described in Infectious Diseases: General Problems. Immunization registries—confidential, population-based, computerized information systems that collect vaccination data about all residents of a geographic area—can be used to increase and sustain high vaccination coverage.

See Related Guideline from CURRENT Practice Guidelines in Primary Care 2006

Skin testing for tuberculosis and treating selected patients reduce the risk of reactivation tuberculosis (see Table 9–12). Attention to technique helps separate negative from positive results. A more precise measurement of induration from the PPD can be obtained by drawing a line on the skin with a medium ballpoint pen, starting 1–2 cm away from the skin reaction and then stopping when resistance is felt. Patients with HIV infection are at an especially high risk for tuberculosis. This is discussed in Infectious Diseases: HIV, as is multidrug-resistant tuberculosis.

HIV infection is now the major infectious disease problem in the world, and it affects 850,000–950,000 persons in the United States. Since sexual contact is a common mode of transmission, primary prevention relies on eliminating unsafe sexual behavior by promoting abstinence, later onset of first sexual activity, decreased number of partners, and use of latex condoms. Appropriately used, condoms can reduce the rate of HIV transmission by nearly 70%. In one study, couples with one infected partner who used condoms inconsistently had a considerable risk of infection: the rate of seroconversion was estimated to be 13% after 24 months. No seroconversions were noted with consistent condom use. Unfortunately, as many as one-third of HIV-positive individuals continue unprotected sexual practices after learning that they are HIV-infected. Tailored group educational intervention focused on practicing "safer sex" can reduce their transmission-risk behaviors with partners who are not HIV-positive. Other approaches to prevent HIV infection include treatment of sexually transmitted diseases, development of vaginal microbicides, and vaccine development. Increasingly, cases of HIV infection are transmitted by injection drug use. HIV prevention activities should include provision of sterile injection equipment for these individuals.

With regard to secondary prevention, many HIV-infected persons in the US currently receive the diagnosis at advanced stages of immunosuppression, and almost all will progress to AIDS if untreated. On the other hand, highly active antiretroviral therapy (HAART) substantially reduces the risk of clinical progression or death in patients with advanced immunosuppression. Screening tests for HIV are extremely (> 99%) accurate. While the benefits of HIV screening appear to outweigh its harms, current screening is generally based on individual patient risk factors. Such screening can identify persons at risk for AIDS but misses a substantial proportion of those infected. Nonetheless, the yield from screening higher prevalence populations is substantially greater than that from screening the general population, and more widespread screening of the population remains controversial.

In immunocompromised patients, live vaccines are contraindicated but many killed or component vaccines are safe and recommended. Asymptomatic HIV-infected patients have not shown adverse consequences when given live MMR and influenza vaccinations as well as tetanus, hepatitis B, H influenzae type b, and pneumococcal vaccinations—all should be given. However, if poliomyelitis immunization is required, the inactivated poliomyelitis vaccine is indicated. In symptomatic HIV-infected patients, live virus vaccines such as MMR should generally be avoided, but annual influenza vaccination is safe.

Whenever possible, immunizations should be completed before procedures that require or induce immunosuppression (organ transplantation or chemotherapy), or that reduce immunogenic responses (splenectomy). However, if this is not possible, the patient may mount only a partial immune response, yet even this partial response can be of benefit. Patients who undergo allogeneic bone marrow transplantation lose preexisting immunities and should be revaccinated. In many situations, family members should also be vaccinated to protect the immunocompromised patient, although oral live polio vaccine should be avoided because of the risk of infecting the patient.

New cases of poliomyelitis have been reported in the United States, Haiti and the Dominican Republic recently, slowing its eradication in the Western Hemisphere.

The 2001 anthrax attacks in the United States have raised concern about the nation's vulnerability to a smallpox attack. Resumption of smallpox vaccination was undertaken for some health care workers, police and firemen, etc. However, smallpox vaccine has a higher complication rate than any other vaccine currently being used. Expected adverse events in a mass smallpox vaccination campaign include fever (less than one case per five vaccine recipients), rash (less than one case per one hundred recipients), encephalitis (less than three cases per million), and death (less than two cases per million). Careful prevaccination exclusion of high-risk individuals (those with eczema or immunosuppression or coronary artery disease) is essential to minimize such complications.

During the 2002–2004 smallpox vaccination campaign, only 214 neurologic events were reported among 665,000 persons vaccinated against smallpox, and these were generally mild and self-limited. Serious neurologic events, such as postvaccinal encephalitis, Bell's palsy, and Guillain-Barré syndrome, occurred with expected incidences. No neurologic sequelae were identified at a rate above baseline estimates. In terms of overall complications, among 37,901 volunteers receiving 38,885 doses of smallpox vaccine in 2003, there were 100 serious adverse events reported, resulting in 85 hospitalizations, 10 life-threatening illnesses, 2 permanent disabilities, and 3 deaths. Among the serious adverse events, there were 21 cases of myocarditis, pericarditis, and ischemic cardiac events. Serious adverse events were more common among older persons being revaccinated than among younger persons being vaccinated for the first time. Rigorous smallpox vaccine safety screening and educational programs contributed to low rates of preventable life-threatening adverse reactions.

The current epidemic of highly pathogenic H5N1 avian influenza within duck and poultry populations in Southeast Asia raises serious concerns that genetic reassortment will result in a human influenza pandemic. In 2003 through 2005, there were 138 confirmed cases of human infection with H5N1 avian influenza in Vietnam, Thailand, Indonesia, China, and Cambodia, with a mortality rate of > 50%. To prevent and prepare for an increase in human cases, public health officials are working to improve detection methods and to stockpile effective antivirals, such as oseltamivir. While vaccines are the mainstay of prophylaxis against influenza, there are technical and safety issues that must be overcome in the development of an avian influenza vaccine for use in humans.