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. Recommended immunization schedules for children and adolescents can be found online at http://www.cdc.gov/vaccines/recs/schedules/child-schedule .htm and the schedule for adults is outlined in Table 30–7. 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. Strategies to enhance vaccinations include increasing community demand for vaccinations; enhancing access to vaccination services; and provider- or systembased interventions, such as reminder systems.

Evidence suggests annual influenza vaccination is safe and effective with potential benefit in all age groups, and the Advisory Committee on Immunization Practices (ACIP) recommends routine influenza vaccination for all persons aged 6 months and older, including all adults. When vaccine supply is limited, certain groups should be given priority, such as adults 50 years and older, individuals with chronic illness or immunosuppression, and pregnant women. An alternative high-dose inactivated vaccine for adults 65 years and older is available. This inactivated trivalent vaccine contains 60 mcg of hemagglutinin antigen per influenza vaccine virus strain (Fluzone High-Dose [Sanofi Pasteur]). Adults 65 years and older can receive either the standard dose or high-dose vaccine, whereas those younger than 65 years should receive a standard-dose preparation.

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 available for use in adolescents and in adults younger than 65 years. Compared with DTaP, which is used in children under the age of 7, Tdap has a reduced dose of the diphtheria and pertussis vaccines. The ACIP recommends 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). Due to increasing reports of pertussis in the United States, clinicians may choose to give Tdap to persons aged 65 years and older despite limited published data on the safety and efficacy of the vaccine in this age group.

Both hepatitis A vaccine and immune globulin provide protection against hepatitis A; however, administration of immune globulin may provide a modest benefit over vaccination in some settings. A recombinant protein hepatitis E vaccine has been developed that has proven safe and efficacious in preventing hepatitis E among highrisk populations.

Human papillomavirus (HPV) virus-like particle (VLP) vaccines have demonstrated effectiveness in preventing persistent HPV infections, and thus may impact the rate of cervical intraepithelial neoplasia (CIN) II–III. The American Academy of Pediatrics (AAP) recommends routine HPV vaccination for girls aged 11–12 years. The AAP also recommends that all unvaccinated girls and women ages 13–26 years receive the HPV vaccine. It is estimated that routine use of HPV vaccination of females at 11 to 12 years of age and catch-up vaccination of females at age 13–16 (with vaccination of girls age 9 and 10 at the discretion of the physician) could prevent 95% to 100%  of CIN and adenocarcinoma in situ, 99% of genital warts and approximately 70% of cervical cancer cases worldwide; thus, the role of HPV testing will need redefinition. In October 2011, the ACIP approved recommendations for routine vaccination of males 11 or 12 years of age with three doses of HPV4 (quadrivalent vaccine). Vaccination of males with HPV may lead to indirect protection of women by reducing transmission of HPV. Despite the effectiveness of the vaccine, rates of immunization are low. Interventions addressing personal beliefs and system barriers to vaccinations may help address the slow adoption of this vaccine.

Persons traveling to countries where infections are endemic should take precautions described in Chapter 30. 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.

 Skin testing for tuberculosis (see Table 9–16) and treating selected patients reduce the risk of reactivation tuberculosis. Two blood tests, which are not confounded by prior BCG (bacille Calmette-Guérin) vaccination, have been developed to detect tuberculosis infection by measuring in vitro T-cell interferon-gamma release in response to two antigens (the enzyme-linked immunospot [ELISpot], [T-SPOT.TB] and the other, a quantitative ELISA [QuantiFERON-TBGold] test). These T-cell–based assays have an excellent specificity that is higher than tuberculin skin testing in BCG-vaccinated populations. The rate of tuberculosis in the United States has been declining since 1992. In 2009, the US tuberculosis rate was 3.8 cases per 100,000 population, a decrease of 11.4% from the 2008 rate (4.2 per 100,000). This represents the greatest single-year decrease ever recorded and was the lowest
recorded rate since national tuberculosis surveillance began in 1953.

The Advisory Council for the Elimination of Tuberculosis has called for a renewed commitment to
eliminating tuberculosis in the United States, and the Institute of Medicine has published a detailed plan for achieving that goal. Patients with HIV infection are at an especially high risk for tuberculosis, and tuberculosis preventive therapy in the era of HIV will require further work to overcome implementation barriers and to identify optimal duration of preventive therapy and treatment approach for individuals receiving highly active antiretroviral therapy (HAART).

Treatment of tuberculosis poses a risk of hepatotoxicity and thus requires close monitoring of liver transaminases. Alanine aminotransferase (ALT) monitoring during the treatment of latent tuberculosis infection is recommended for certain individuals (preexisting liver disease, pregnancy, chronic alcohol consumption). ALT should be monitored in HIV-infected patients during treatment of tuberculosis disease and should be considered in patients over the age of 35. Symptomatic patients with an ALT elevation three times the upper limit of normal (ULN) or asymptomatic patients with an elevation five times the ULN should be treated with a modified or alternative regimen.

In 2010, the Centers for Disease Control and Prevention (CDC) updated guidelines for the prevention and treatment of sexually transmitted diseases. Highlights of these guidelines include updated treatments for bacterial vaginosis and genital warts as well as antibiotic-resistant Neisseria gonorrhoeae, the prevalence of which has risen.

HIV infection is a 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 persons continue unprotected sexual practices after learning that they are HIV-infected. Preexposure prophylaxis with antiretroviral drugs in men who have sex with men could have a major impact on preventing HIV infection, and studies evaluating the impact in other groups are underway. Postexposure prophylaxis is widely used after occupational and nonoccupational contact, and it has been estimated to reduce the risk of transmission by approximately 80%.

With regard to secondary prevention, many HIVinfected persons in the United States receive the diagnosis at advanced stages of immunosuppression, and almost all will progress to AIDS if untreated. On the other hand, 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 influenza 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 beneficial. 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.

Herpes zoster, caused by reactivation from previous varicella zoster virus (VZV) infection, affects many older adults and people with immune system dysfunction. Whites are at higher risk than other ethnic groups and the incidence in adults age 65 and older may be higher than previously described. It can cause postherpetic neuralgia, a potentially debilitating chronic pain syndrome. A varicella vaccine is available for the prevention of herpes zoster. Several clinical trials have shown that this vaccine (Zostavax) is safe, elevates VZV-specific cell-mediated immunity, and significantly reduces the incidence of herpes zoster and postherpetic neuralgia in persons older than 60 years. In one randomized, double-blind, placebo-controlled trial among more than 38,000 older adults, the vaccine reduced the incidence of postherpetic neuralgia by 66% and the incidence of herpes zoster by 51%. The ACIP recommends routine zoster vaccination, administered as a one-time subcutaneous dose (0.65 mL), of all persons aged 60 years or older. Persons who report a previous episode of zoster can
be vaccinated; however, the vaccine is contraindicated in immunocompromised (primary or acquired) individuals. The durability of vaccine response and whether any booster vaccination is needed are still uncertain. The cost effectiveness of the vaccine varies substantially, and the patient’s age should be considered in vaccine recommendations. One study reported a cost-effectiveness exceeding $100,000 per quality-adjusted life year saved. Despite its availability, uptake of the vaccine remains low at 2–7% nationally. Financial barriers (cost, limited knowledge of reimbursement) have had a significant impact on its underutilization.

 Methicillin-resistant Staphylococcus aureus (MRSA), previously recognized as a nosocomial pathogen, has emerged as a common cause of staphylococcal infection in the outpatient setting; it accounts for more than 50% of outpatient staphylococcal infections. Community-acquired (CA)-MRSA strains affect healthy individuals, and the burden of disease can range from a furuncle to more severe life-threatening infections. Treatment of CA-MRSA is different from nosocomial MRSA because CA-MRSA strains typically retain susceptibility to antibiotics that are ineffective in treating nosocomial strains.