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Update: Influenza Activity -- New York and United States, 1994-95 Season

Influenza activity in the United States during the current influenza season began in the Northeast, and during late January, spread to other regions of the country. This report describes influenza outbreaks in nursing homes in New York and summarizes national influenza surveillance data from October 2, 1994, through February 11, 1995. New York

The first influenza outbreak reported to CDC during the 1994- 95 season occurred in a 300-bed skilled-nursing facility in Long Island, New York. On November 30, 1994, eight residents on one 20-bed corridor developed influenza-like illness (ILI) (i.e., fever greater than or equal to 100 F {greater than or equal to 38 C} and cough). On December 1, nasopharyngeal swab specimens from these eight residents were submitted for rapid antigen testing; within 5 hours after transport to the laboratory, influenza type A was detected by enzyme immunoassay in six specimens. On the evening of December 1, 293 of the 299 residents in the facility each received 100 mg of amantadine hydrochloride as treatment for the eight ill residents and as prophylaxis against influenza A infection for the other 285 residents. Most (285 {95%}) residents had received influenza vaccine before the outbreak. On December 2, as part of the nursing home's contingency plan for influenza outbreaks, amantadine dosages were modified for individual residents based on estimated creatinine clearance (1,2), and prophylaxis was continued for 14 days. Other outbreak-control measures included confining ill residents to their rooms for at least 72 hours after the initiation of amantadine treatment and prophylaxis, confining all residents to their individual units, suspending group activities, and minimizing the assignment of nursing staff to multiple units. The amantadine dosage subsequently was discontinued for five residents and reduced for 13 residents because of side effects (primarily confusion and agitation); for most patients, side effects resolved within 48 hours of dosage adjustment.

During the first 48 hours of amantadine prophylaxis and treatment, six additional residents developed ILI. Of the 14 residents who developed outbreak-associated ILI, five subsequently developed clinical pneumonia. During the 2-week period of amantadine prophylaxis, sporadic cases of febrile respiratory illness occurred in other units of the facility; however, there was no clustering of cases.

Tissue culture of all eight nasopharyngeal specimens yielded influenza type A(H3N2). These isolates were further characterized at CDC; all were antigenically similar to the A/Shangdong/09/93 strain included in the 1994-95 influenza vaccine.

Influenza surveillance in New York state indicated increasing activity beginning in late November 1994. From December 1, 1994, through February 11, 1995, outbreaks associated with influenza type A(H3N2) in 46 other nursing homes were reported to the New York State Department of Health (NYSDOH); of these, 16 were reported from nursing homes in Long Island. For all 16 facilities, influenza type A infection was documented by rapid antigen detection; in 13 facilities, amantadine was administered as an outbreak-control measure. Outbreaks in five other nursing homes were caused by influenza type B and, in two nursing homes, by influenza types A and B. Based on findings of virologic surveillance in New York, influenza has occurred in persons in all age groups during the 1994-95 season. Of the 385 influenza virus isolates reported by laboratories in New York this season, 332 (86%) have been type A. United States

From November 27, 1994, through January 21, 1995, most influenza activity was reported from the Northeast (3). However, during January 22-February 11, regional or widespread activity was reported from states in every region.

Through February 11, World Health Organization collaborating laboratories reported 1282 influenza virus isolates; of these, 923 (72%) isolates have been type A and 359 (28%) have been type B. Of the influenza A isolates that have been subtyped, all have been type A(H3N2).

The proportion of deaths attributable to pneumonia and influenza reported from 121 U.S. cities slightly exceeded the epidemic threshold during six of the 19 weeks from October 2, 1994, through February 11, 1995, but has not exceeded the threshold for any 2 consecutive weeks. Reported by: IH Gomolin, MD, Gurwin Jewish Geriatric Center, Commack, New York; HB Leib, MS, RJ Gallo, S Kondracki, G Brady, G Birkhead, MD, DL Morse, MD, State Epidemiologist, New York State Dept of Health. Participating state and territorial epidemiologists and state public health laboratory directors. World Health Organization collaborating laboratories. Sentinel Physicians Influenza Surveillance System of the American Academy of Family Physicians. WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Influenza vaccination is 70%-90% effective in preventing ILI in young, healthy adults when the vaccine antigens closely match the circulating influenza virus strains. Because of the decreased immunologic response among the elderly, the vaccine is less effective in preventing the occurrence of ILI in nursing home residents (i.e., 30%-40% effective) (4). However, vaccination of nursing home residents is associated with a substantial (i.e., 50%-60% effectiveness) reduction in the occurrence of serious complications and hospitalization and with preventing death (up to 80% effective); in addition, vaccination reduces the risk for outbreaks in nursing home settings (4,5). Antiviral agents are recommended as an adjunct to vaccination in controlling influenza type A. To control influenza A outbreaks in the nursing home setting, antiviral drugs should be administered to all residents, regardless of influenza vaccination status.

Influenza outbreak-control measures used in the New York nursing home (e.g., rapid influenza A antigen detection and prompt initiation of antiviral treatment and prophylaxis to all residents) were based on recommendations of the Advisory Committee on Immunization Practices (ACIP) (3,6) and CDC and are actively promoted by NYSDOH. Although annual influenza vaccination of nursing home residents is considered a standard of care, use of antiviral agents as an adjunct to vaccination is less common, reflecting, in part, concern about side effects and, until recently, the protracted time required for laboratory confirmation of influenza type A.

The use of amantadine as an adjunct for the control of influenza type A outbreaks in New York during the current season illustrates the usefulness of education about and promotion of the use of antiviral agents and rapid influenza diagnostic methods. In September 1994, NYSDOH mailed information to all health-care facilities in New York urging health-care providers to administer vaccine in accordance with the recommendations of the ACIP, to use rapid antigen-detection testing and viral culture when institutional outbreaks of ILI are initially recognized, and to use amantadine when appropriate. On December 20, the NYSDOH sent an electronic mail message to these institutions to report the rapid identification of influenza type A in the first nursing home outbreak and to reinforce the recommendations for influenza control measures in health-care facilities.

Recommendations of the ACIP for use of amantadine and rimantadine, the two antiviral drugs currently available for treatment and prophylaxis of influenza type A, were published in MMWR on December 30, 1994 (4). These recommendations also provide information for assisting health-care providers in selecting the appropriate drug for specific patient groups but do not recommend preferential use of either drug.

As influenza activity continues to increase in the United States, health-care providers should be informed about findings of local, state, and national influenza surveillance and be familiar with methods for rapid viral diagnosis. Updated information about national influenza surveillance is available through the CDC Information System by voice or fax (404) 332-4551. In addition, providers should develop contingency plans to control influenza outbreaks that include the use of rapid diagnosis. When possible, policy decisions regarding use of amantadine and rimantadine should be made before outbreaks occur.


  1. Gomolin IH, Leib HB, Arden NH, Sherman FT. Control of influenza outbreaks in the nursing home: guidelines for diagnosis and management. J Am Geriatr Soc 1995;43:71-4.

  2. ACIP. Prevention and control of influenza: part II, antiviral agents -- recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1994;43(no. RR-15).

  3. CDC. Update: influenza activity -- United States, 1994-95 season. MMWR 1995;44:84-6.

  4. Arden NH, Patriarca PA, Kendal AP. Experiences in the use and efficacy of inactivated influenza vaccine in nursing homes. In: Kendal AP, Patriarca PA, eds. Options for the control of influenza. New York: Alan R. Liss, 1986:155-68.

  5. Patriarca PA, Weber JA, Parker RA, et al. Efficacy of influenza vaccine in nursing homes: reduction in illness and complications during an influenza A(H3N2) epidemic. JAMA 1985;253: 1136-9.

  6. ACIP. Prevention and control of influenza: part I, vaccines -- recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1994;43(no. RR-9).

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