Prevention and Management of Influenza in the Nursing Home Population
Kay E. Schwebke, MD, MPH

An influenza outbreak is a significant threat to any long-term care facility. Several measures can be taken to prevent as well as limit the extent and severity of disease. Achieving high vaccination rates among residents, staff members, volunteers, and visitors with extensive resident contact will clearly enhance primary prevention. In addition, staff education, rapid diagnosis, infection-control measures, and antiviral medications may reduce the spread of the disease. Because swift implementation of these steps is important, contingency planning is recommended.

(Annals of Long-Term Care 1999;7[12]:443-446)

Among adults, influenza is responsible for approximately 20,000 deaths annually in the United States and for 110,000 excess hospitalizations.1 During epidemic years, these numbers are much higher. An influenza outbreak can be devastating in a closed population such as in a long-term care facility. In this article, several important issues related to influenza will be reviewed, including epidemiologic characteristics, prevention strategies, and outbreak identification and control.

Epidemiology

The definition from the Centers for Disease Control and Prevention of an influenza-like illness is a fever (>= 100° F oral or >= 101° F rectal) and at least one of the following respiratory signs or symptoms: cough, rhinorrhea, nasal congestion, or sore throat. A cluster is defined as three or more cases of an influenza-like illness on a single nursing unit within 48 to 72 hours.2 Symptoms are typically acute but may be vague and nonspecific. The clinical diagnosis may be assisted by knowledge of local influenza activity, information that is available from state health department representatives.

Influenza epidemics generally peak between December and March each year in temperate regions of the Northern Hemisphere. However, sporadic cases and occasionally large outbreaks can occur at other times of the year. Both influenza A and influenza B may be responsible for epidemics; however, influenza A is more common.3 This fact is important because the antiviral medications amantadine and rimantadine, which are commonly used for prophylaxis and treatment, are effective only against influenza A.

Recognizing the early signs and symptoms of influenza is crucial to early diagnosis and outbreak control. The incubation period is short, typically one to four days. An influenza outbreak is characterized by an abrupt onset, with peak activity within two to three weeks and a total duration of five to eight weeks. Second and third waves of the disease may occur,4 with the same viral strain usually involved.

Prevention

Vaccinating persons before the influenza season each year is the most effective way of reducing influenza cases. Among persons residing in long-term care facilities, studies have demonstrated that the influenza vaccine is 30% to 40% effective in preventing illness, 50% to 60% effective in preventing hospitalization and pneumonia, and 80% effective in preventing death.5 The optimal time to vaccinate is from October through mid-November.1 However, vaccination can continue throughout the respiratory infection season.

Vaccination should be provided to all residents of long-term care facilities. Vaccination rates can be improved by obtaining consent for vaccination at the time of a resident's admission to the facility. Residents admitted to the facility after the vaccination program should be vaccinated if there is no proof of previous vaccination. Staff members, volunteers, and visitors with extensive resident contact should be educated about the influenza vaccine and should be strongly encouraged to receive it.

Identification and Control

Swift control of an influenza outbreak is facilitated by active surveillance, rapid diagnosis, aggressive infection-control practices, and prompt treatment and chemoprophylaxis. Active surveillance can be enhanced through staff member education during the month of October. All staff members should be included in this educational campaign. This program represents an excellent opportunity to review presenting signs and symptoms of an influenza-like illness, to reinforce the value of vaccination, and to discuss influenza-control practices. Ideally, this timely education will enhance detection of early influenza cases through increased awareness and appropriate use of diagnostic tests.

Diagnosis

Once the diagnosis of influenza is considered, appropriate diagnostic tests such as cultures or rapid tests can be ordered. Cultures. The gold standard diagnosis of influenza involves a traditional viral culture. Not only does the culture confirm an influenza case, but it may assist with the diagnosis of other viral pathogens. One major disadvantage of the culture, however, is the slow availability of test results, often taking five to 10 days.

Rapid Tests. In certain situations, more rapid diagnosis of influenza may assist with decisions about the use of antiviral medications, particularly in the setting of acute influenza treatment (initiated within 48 hours of symptom onset) or outbreak control (eg, in long-term care facilities). Early diagnosis may be possible using a rapid diagnostic test. These tests employ immunochemical techniques, including direct and indirect immunofluorescence and enzyme immunoassay, to detect viral proteins.

The performance of various diagnostic tests as compared with viral culture has been evaluated. For the rapid diagnostic tests designed to detect influenza A only, the sensitivity ranges from 86% to 92%, and the specificity from 97% to 99%.6 For the newer rapid diagnostic tests designed to detect influenza A and B, the sensitivity ranges from 62% to 88%, and the specificity from 95% to 99%.7 Although false-negative test results are a problem, false-positive results are less common. The advantages of these tests include rapid performance (less than 20 minutes on average) and an approximate cost of $40.00 to $50.00 per test. Disadvantages include the frequent need to obtain a simultaneous viral culture, dependence on adequate sampling technique, potential for inappropriate use, and the relative lack of clinical experience with these tests.

For most of these diagnostic tests, the best sampling method is with a nasopharyngeal wash or aspiration; throat and nasopharyngeal swabs have a lower yield.6,7 However, collection with throat and nasopharyngeal swabs are often more practical, easier to use, and may be safer when attempting to collect specimens from residents of long-term care facilities.

Infection Control

It is often necessary to initiate infection-control measures and antiviral medications while awaiting the results of diagnostic tests. Even though the actual time to complete the rapid diagnostic test is 20 minutes, the sample is typically sent to a reference laboratory with an actual turnaround time of 24 to 48 hours. If several residents are reporting influenza-like symptoms, collecting the rapid diagnostic test specimen along with a viral culture from three to five symptomatic residents may increase the diagnostic yield. Collecting samples from residents who are able to allow adequate specimen collection (ie, alert, noncombative, relatively free of cognitive impairment) may decrease sampling errors.

If the rapid test is positive for influenza, then infection-control practices should be followed and antiviral medications prescribed as described below. A positive influenza culture would be expected in this situation. This additional culture information would clarify the diagnosis as well as provide valuable surveillance information about circulating influenza strains. If the rapid test is negative for influenza but clinical suspicion of an influenza-like illness is high, the differential diagnosis will need to include influenza with a false-negative test result or other pathogens.

Appropriate infection-control measures should continue while awaiting culture results. Decisions about antiviral medications will need to be individualized and made before culture results are available. Assistance from an infectious disease specialist or a representative of the state health department may be helpful in this difficult situation.

As soon as a cluster of influenza-like cases is identified, aggressive infection-control practices should begin, including consideration of antiviral medication treatment and chemoprophylaxis. The mode of transmission for influenza involves small-particle aerosolization; particles are typically expelled into the air when a person coughs, talks, or sneezes. Transmission by direct contact may also occur.4 Given these well- established modes of transmission, simple infection-control practices should include consistent hand washing when interacting with all residents, as well as the use of masks, gloves, and gowns for direct patient care involving symptomatic residents. In addition, careful isolation of suspected cases and cohorting of cases whenever possible is recommended. Visitors to the facility should be limited, social gatherings postponed, and symptomatic staff members and visitors discouraged from interacting with residents. These practices can begin before an influenza case is actually confirmed. In fact, these infection-control steps will be helpful in limiting the transmission of many respiratory pathogens.

Vaccination

Resident and staff influenza vaccination status should be reviewed, and antiviral medication use should be discussed. If a case of influenza is confirmed or highly suspected, previously unvaccinated persons for whom there are no contraindications for the influenza vaccine--including residents, staff members, and frequent visitors--should be strongly encouraged to receive the vaccine. When influenza is confirmed or highly suspected, antiviral medications should be initiated as soon as possible.

Antiviral Medications

Several important issues must be kept in mind when considering and providing influenza antiviral medications. With a potential or confirmed influenza outbreak, many steps need to be taken very quickly, with advance planning of extreme value in ensuring efficient and effective response. Preapproved medication orders for chemoprophylaxis can enhance rapid initiation of these medications.

Amantadine and rimantadine are the two antiviral medications that are currently available and typically used in this situation. When antiviral medications are started, they should be provided to all residents, regardless of whether they received the influenza vaccine the previous fall, assuming that there are no contraindications for medication use.1 Chemoprophylaxis should also be considered for all staff members.

Indications. Amantadine and rimantadine are chemically related medications that interfere with the replication of influenza type A viruses. They are not effective against influenza B or other viral respiratory pathogens. They can be used for both treatment and prevention (ie, chemoprophylaxis) of influenza A infection. When used for treatment, they should be initiated within 48 hours of illness onset. In this situation, three to five days of treatment is recommended, or discontinuation of the medication 24 to 48 hours after resolution of signs and symptoms. When used for chemoprophylaxis, these medications can be started at any time, although rapid initiation can limit the spread of disease. Chemoprophylaxis should be continued for at least two weeks, or until at least one week after the end of the outbreak.1

Side Effects. Amantadine and rimantadine can cause adverse reactions in some persons. Serious side effects can include delirium, hallucinations, behavioral changes, agitation, seizures, dizziness, ataxia, and falls. In addition, nausea, anorexia, insomnia, and fatigue may be reported or observed.

These medications do differ in their pharmacokinetic properties. More than 90% of amantadine is excreted unchanged in the urine, whereas approximately 75% of rimantadine is metabolized by the liver. The appropriate medication dose depends on several factors, including an individual's age, renal and liver function, and indications for medication use. A summary of common doses has been published previously.4

The incidence of central nervous system side effects is lower among persons taking rimantadine than among those taking amantadine.8 However, this advantage may be offset by the higher cost of rimantadine. Additional clinical factors may assist the physician in determining the specific medication to use.

Neuraminidase Inhibitors

The new selective neuraminidase inhibitors zanamivir and osteltamivir will offer another class of medications to consider when initiating antiviral treatment. These medications are effective against both influenza A and B. They are FDA-approved for treatment only and are more expensive than amantadine and rimantadine. Although they are not currently licensed for the prevention of influenza, data suggest that these medications are effective for chemoprophylaxis.9-11 The availability of these new medications may significantly impact the management of influenza infections, particularly when influenza B is involved. Future studies likely will improve our understanding of the role of these medications in the setting of an influenza outbreak.

If an outbreak does occur in a facility, it can be instructive to review the response and outcome at a subsequent staff meeting. This is an excellent opportunity to reinforce approaches that were successful as well as to understand any problems that occurred.

Summary

The development of an influenza outbreak is a significant threat to any long-term care facility. Several measures can be taken to prevent as well as limit the extent and severity of disease. Achieving high influenza vaccination rates among residents and staff members will clearly enhance primary prevention. In addition, staff member education, rapid diagnosis, the implementation of infection-control policies, and the use of antiviral medications may reduce the spread of disease. Since rapid implementation of these steps is important, contingency planning is recommended to facilitate a comprehensive and efficient response.

About the Author

Dr. Schwebke is board-certified in Internal Medicine and Infectious Diseases, Allina Medical Clinic (Northfield, MN) and Hennepin County Medical Center (Minneapolis). Address for correspondence: Kay E. Schwebke, MD, MPH, Allina Medical Clinic–Northfield, 1400 Jefferson Rd, Northfield, MN 55057.

References

1.Prevention and control of influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep 1999;48(RR-4):1-28.

2.Gomolin I, Leib H, Arden N, Sherman F. Control of influenza outbreaks in the nursing home: Guidelines for diagnosis and management. J Am Geriatr Soc 1995;43:71-74.

3.Update: Influenza activity--United States and worldwide, 1998-99 season, and composition of the 1999-2000 influenza vaccine. MMWR Morb Mortal Wkly Rep 1999;48(18):374-378.

4.Cox N, Fukuda K. Influenza. Infect Dis Clin North Am 1998;12(1):27-38.

5.Prevention and control of influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep 1998;47(RR-6):1-26.

6.Leonardi GP, Leib H, Birkhead GS, et al. Comparison of rapid detection methods for influenza A virus and their value in health-care management of institutionalized geriatric patients. J Clin Microbiol 1994;32(1):70-74.

7.Influenza diagnostic testing comparison. ZymeTx, Inc, Oklahoma City, OK; 10/99.

8.Dolin R, Reichman R, Madore H, et al. A controlled trial of amantadine and rimantadine in the prophylaxis of influenza A infection. N Engl J Med 1982;307:580-584.

9.Aoki F, Osterhaus A, Rimmelzwaan G, et al. Oral GS4104 successfully reduces duration and severity of naturally acquired influenza. In: Program and abstracts of the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy; September 24-27, 1998; Washington, DC. Abstract LB-5.

10.Schilling M, Povinelli L, Krause P, et al. Efficacy of zanamavir for chemoprophylaxis of nursing home influenza A outbreaks. In: Program and abstracts of the 37th Interscience Conference on Antimicrobial Agents and Chemotherapy; September 28-October 1, 1997; Toronto, Canada. Abstract H-92.

11.Hayden F, Atmar R, Schilling M, et al. Use of the selective oral neuraminidase inhibitor osteltamivir to prevent influenza. N Engl J Med 1999;341:1336-1343.

Annals of Long-Term Care - ISSN: 1524-7929 - Volume 7 - Issue 12 - December 1999