INFECTION CONTROL NEWSLETTER

January 1997
written by and for Long Term Care Infection Control Nurses

Broad Street Solutions
James Marx, RN, MS, CIC Editor
PO Box 16557
San Diego, CA 92176
(619)563-0274 Voice/FAX
jmarx@concentric.net

ESTABLISHING BASELINE INFECTIONS LEVELS AND THRESHOLDS

Infection Control surveillance consists of data collection and analysis. The interpretation of the number of infections is critical in order to make use of the information collected. Using the facilities historical infection surveillance data, you can establish a baseline infection level which is site-specific. Next you apply a statistical test to see if the current month's number of infections exceeds the expected number. If your facility has a stable resident population, you can calculate the average number of lower respiratory tract infections (LRI) per month. For example, if there are an average of 3.5 LRI's per month, the threshold would be 7 (p = .05). The p value here means there is a 5% or less chance that 7 LRI cases would be by random chance alone. If in one month there were 8 LRI cases, this would prompt an epidemiologic investigation. If there were less than 7 LRI cases in one month, no further investigation would be needed. If you use this table, you will be able to interpret you infection surveillance data with statical significance.

THRESHOLD NUMBERS FOR AN INFECTION ALERT

Endemic Level
	p = 0.10	p = 0.05	p = 0.01
0.5	2	3	3
1	3	4	4
1.5	4	4	5
2	4	5	6
2.5	5	6	7
3	5	6	8
3.5	6	7	8
4	6	8	9
4.5	7	8	10
5	7	9	11
6	8	10	12
7	9	11	13
8	10	12	14
9	11	13	16
10	12	14	17

Original chart can be found in
Childress JA, Childress JD. Statistical test for possible infections outbreaks. Infection Control 1981;2:247-249.

Decreased Antibody Response to Influenza Vaccine Among Nursing-Home Residents Who Received Recalled Vaccine

As reported in the December 20, 1996 MMWR

Following a voluntary recall in November 1996 of 11 lots* of Fluogen Ć trivalent influenza vaccine (Parke-Davis Division, Warner Lambert Company), the New York State Department of Health and CDC evaluated antibody response to the 1996‚97 influenza vaccine among residents (n=86) of three nursing homes who received recalled vaccine and among residents (n=86) of three other nursing homes who received vaccine produced by a different manufacturer. The Fluogen Ć lots were recalled because the monitored quantity of A/Nanchang/933/ 95(H3N2) hemagglutinin antigen in the 1996‚97 influenza vaccine had declined since the vaccine initially was released; the reason for this decrease is unknown. The findings of this analysis indicate that, compared with elderly nursing-home residents who received influenza vaccine from a different manufacturer, residents who received Fluogen Ć from recalled lots had moderately lower antibody responses to the influenza A/Nanchang/ 933/95(H3N2) component of the 1996‚97 influenza vaccine. Medical records were reviewed for and blood samples were obtained from the 172 nursing-home residents who received influenza vaccine. Postvaccination serum samples were analyzed for antibody against all three components of the 1996‚97 vaccine. For the group of residents that received recalled vaccine, antibody titers against the A/Nanchang /933/95(H3N2) vaccine component were significantly lower than for the group of residents that received vaccine from a different manufacturer. For both groups of residents, antibody titers were similar for the B/Harbin/07/94 and A/Texas/ 36/91(H1N1) vaccine components. The analysis also assessed demographic characteristics, chronic medical conditions, previous vaccination status, and activity levels; however, none of these factors accounted for the group-specific differences in antibody titers.

CDC Editorial Note: Based on the finding in New York that antibody response among nursing-home residents who received recalled Fluogen Ć was moderately lower than that among residents who received influenza vaccine from a different manufacturer, health-care providers might consider revaccinating persons who received recalled Fluogen Ć . Several factors have been considered for determining whether persons who received recalled Fluogen Ć should receive an additional dose of the 1996‚97 in-fluenza vaccine. First, although higher postvaccination antibody levels generally are associated with greater protection from influenza-like illness and its complications, there is no absolute antibody titer that ensures protection. Second, because revaccination does not ensure development of higher antibody titers, it is difficult to estimate the potential clinical and public health benefits associated with revaccina-tion. Finally, a recent study of young adults indicated that antibody titers did not differ among groups randomized to receive either recalled or nonrecalled Fluogen Ć manu-factured for the 1996‚97 influenza season. Although the total number of persons who received vaccine from recalled lots of Fluogen Ć represent only 5%‚7% of all persons nationwide who received a 1996‚97 influenza vaccination, most doses of vaccine have been administered before the influenza season (October‚mid-Novem-ber), and all remaining supplies of 1996‚97 vaccine are limited. Based on these factors, CDC and the Food and Drug Administration recommend that physicians consider vaccinating the following persons with the remaining supplies of influenza vaccine, in order of priority: 1) all high-risk persons ( 5 ) who have not received any doses of the 1996‚97 influenza vaccine, especially those with chronic medical conditions; and 2) high-risk persons, especially those with chronic, debilitating medical conditions, who received Fluogen Ć from recalled lots. Revaccinaton is not recommended for other persons, including healthy persons who received Fluogen Ćfrom a recalled lot. An alternative strategy for controlling influenza type A among high-risk patients is the use of the antiviral agents amantadine or rimantadine, especially for chronically ill, institutionalized, or severely debilitated persons who have been or may be exposed to influenza type A during an outbreak. Amantadine and rimantadine are equally effec-tive for prevention and treatment of influenza type A infection. Additional information about the indications, dosage, side effects, and contraindications for these drugs is available in the recommendations of the Advisory Committee on Immunization Practices ( 5 ) and the drug package inserts.

*Lot numbers are 00176P, 00276P, 00576P, 00586P, 00676P, 00686P, 00786P, 00886P, 00966P, 00986P, and 01066P.

REFERENCES

Rota PA, Regnery HL, Kendal AP. Influenza virus. In: Rose NR, de Macario EC, Fahey JL, Fried-man H, Penn GM, eds. Manual of clinical laboratory immunology. 4th ed. Washington, DC: American Society for Microbiology, 1992:57681.
Morris JA, Kasel JA, Saglam M, Knight V, Loda FA. Immunity to influenza as related to antibody levels. N Engl J Med 1966;274:52735.
Arden NH, Patriarca PA, Fasano MB, et al. The roles of vaccination and amantadine prophylaxis in controlling an outbreak of influenza A(H3N2) in a nursing home. Arch Intern Med 1988;148:8658.
Dowdle WR, Coleman MT, Mostow SR, Kaye HS, Schoenbaum SC. Inactivated influenza vac-cines. 2. Laboratory indices of protection. Postgraduate Medical Journal 1973;49:15962.
ACIP. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices. MMWR 1996;45(no. RR-5).