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Respiratory Illness Continued durations reported in this outbreak may be partially due to travel-related factors such as jet lag. Nevertheless, these data suggest that influenza vaccine did not attenuate illness duration in this group.

There are at least three possible reasons for the lack of vaccine efficacy demonstrated: 1) repeated exposures to infectious persons or different dynamics of transmission (11,12) occurring in a population in a partially closed setting may overcome levels of immunity that might be protective in other settings, 2) some of the illnesses may have been caused by other respiratory pathogens circulating at the same time (13), or 3) an influenza virus representing a clinically significant antigenic drift from the vaccine strain caused the outbreak.

The observations in this investigation support the results of laboratory studies (2) that suggest that the A/Leningrad/86(H3N2) component of the vaccine may not provide optimal protection against the strains of virus recently identified in the Pacific Basin and now present in the United States. The need for long-term care facilities housing high-risk patients to develop contingency plans for rapidly initiating amantadine prophylaxis in the event of influenza A outbreaks should be reemphasized (2), particularly in light of continuing reports of influenza A(H3N2) outbreaks in such institutions this winter. References 1. Immunization Practices Advisory Committee. Prevention and control of influenza. MMWR

1987;36:373-80,385-7. 2. Centers for Disease Control. Antigenic variation of recent influenza A(H3N2) viruses. MMWR

1988;37:38-40,46-7. 3. Centers for Disease Control. Outbreak of influenza-like illness in a tour group- Alaska.

MMWR 1987;36:697-8,704. 4. World Health Organization. Influenza. Wkly Epidem Rec 1987;47:359. 5. Olson JG, Ksiazek TG, Irving GS, Rendin RW. An explosive outbreak of influenza caused by

AVUSSR/77-like virus on a United States naval ship. Milit Med 1979;144:743-5. 6. Ksiazek TG, Olsen JG, Irving GS, Settle CS, White R, Petrusso R. An influenza outbreak due

to AIUSSR/77-like (H1N1) virus aboard a US Navy ship. Am J Epidemiol 1980;112:487-94. 7. Moser MR, Bender TR, Margolis HS, Noble GR, Kendal AP, Ritter DG. An outbreak of

influenza aboard a commercial airliner. Am J Epidemiol 1979;110:1-6. 8. Centers for Disease Control. Influenza activity in civilian and military populations and key

points for use of influenza vaccines. MMWR 1986;35:729-31. 9. 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. 10. Barker WH, Mullooly JP. Impact of epidemic type A influenza in a defined adult population.

Am J Epidemiol 1980;112:798-813. 11. Alford RH, Kasel JA, Gerone PJ, Knight V. Human influenza resulting from aerosol

inhalation. Proc Soc Exp Biol Med 1966;122:800-4. 12. Douglas RG Jr. Influenza in man. In: Kilbourne ED, ed. The influenza viruses and influenza.

New York: Academic Press, 1975:395-447. 13. Monto AS, Cavallaro JJ. The Tecumseh study of respiratory illness. II. Patterns of occurrence

of infection with respiratory pathogens, 1965-69. Am J Epidemiol 1971;94:280-9.

Epidemiologic Notes and Reports

Influenza Update

United States

Following are indicators of influenza activity in the United States for the weeks ending January 9, 16, 23, and 30:

Report Week Ending Jan Jan Jan Jan

09 16 23 30 1988 1988 1988 1988

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Influenza-associated morbidity levels reported
by state and territorial epidemiologists

Number of states reporting sporadic activity:*
Number of states reporting regional activity:*

Number of states reporting widespread activity:S
Isolates reported by WHO Collaborating
Laboratories and other laboratories
Cumulative number of states reporting

isolates of influenza A(H3N2): Cumulative number of states reporting

isolates of influenza B: Reports from sentinel physicians Patients seen with influenza-like illness,

expressed as percent of total patient visits: Sentinel physicians reporting outbreaks, expressed as percent of total number of reports received for week: Percentage reporting for week:

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A report on the antigenic properties of recent influenza A(H3N2) viruses can be found in volume 37, number 3 of the MMWR, pages 38-40, 46-47.

*Sporadically occurring cases, no known outbreaks. *Outbreaks in counties whose total population comprises less than 50% of total state population. Outbreaks in counties whose total population comprises 50% or more of total state population. 'Members of the American Academy of Family Physicians who submit weekly influenza surveillance reports based on their patient population.

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* CASES REPORTED

NO REPORTED CASES The Morbidity and Mortality Weekly Report is prepared by the Centers for Disease Control, Atlanta, Georgia, and available on a paid subscription basis from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, (202) 783-3238.

The data in this report are provisional, based on weekly reports to CDC by state health departments. The reporting week concludes at close of business on Friday; compiled data on a national basis are officially released to the public on the succeeding Friday. The editor welcomes accounts of interesting cases, outbreaks, environmental hazards, or other public health problems of current interest to health officials. Such reports and any other matters pertaining to editorial or other textual considerations should be addressed to: Editor, Morbidity and Mortality Weekly Report, Centers for Disease Control, Atlanta, Georgia 30333. Director, Centers for Disease Control

Editor James O. Mason, M.D., Dr.P.H.

Michael B. Gregg, M.D. Director, Epidemiology Program Office

Managing Editor Carl W. Tyler, Jr., M.D.

Gwendolyn A. Ingraham

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The following reports describe two outbreaks of viral gastroenteritis associated with contaminated water.

South Dakota. An outbreak of diarrhea occurred among the 331 participants in an outing held at a South Dakota campground on August 30 and 31, 1986. During the event, in which participants hiked 10 or 20 km, water and a reconstituted soft drink were available at rest stands. The State Department of Health conducted a survey of 181 participants: 135 (75%) of these persons reported a gastrointestinal illness. Symptoms most frequently reported were diarrhea (69%), explosive vomiting (55%), nausea (49%), headache (47%), abdominal cramping (46%), and fever (36%). None of the participants required hospitalization. Attack rates by sex and age of patients were virtually equal. Onset of illness occurred 35 hours (mean) after arrival at the campground, and duration of illness was about 33 hours.

A biotin-avidin immunoassay performed at CDC yielded a fourfold rise in antibody titer to Norwalk virus in seven of 11 paired human serum specimens. No pathogenic bacterial or parasitic agents were identified from stool samples. Illness was strongly associated with the consumption of water or the reconstituted powdered soft drink made with water. No other foodstuffs were implicated. The implicated water came from a well at the campground. A yard hydrant was located next to a septic dump station, where sewage from self-contained septic tanks and portable toilets in the park was collected. Water from this hydrant had been used to fill water coolers and to prepare the powdered soft drink. Laboratory analyses of remaining water and reconstituted soft drink samples showed bacterial contamination (fecal coliforms >1,600 cfu/100 mL). Chlorine was stored in a tank and then drawn directly into the water system by a pump without a monitoring system. Water samples obtained from various locations in the campground had excess coliforms when the chlorination

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES / PUBLIC HEALTH SERVICE

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Viral Gastroenteritis Continued system was not operating. Fluorescent dye injected into a 5,000-gallon septic tank situated uphill from the well confirmed that the well was contaminated with sewage.

This campground was closed immediately and voluntarily by the owner. Corrective measures included relocating the well, installing an alarm system to detect malfunctions in the chlorination system, reconstructing the chlorination system to ensure that chlorine remains in contact with water in a storage tank for 30 minutes before the water is distributed, maintaining a daily log on chlorine residuals and sample collection points, and posting the yard hydrant as a nonpotable source of water.

New Mexico. An outbreak of gastroenteritis occurred among the 92 guests and staff at a cabin lodge in northern New Mexico over the Labor Day weekend in 1986. The guests arrived Friday, August 29, and provided their own food for the weekend. The first persons to become ill developed diarrhea on Saturday morning, within 24 hours after arrival. By Wednesday, 36 of the guests and staff members reported symptoms: 34 had diarrhea; 9, vomiting; 14, fever; 22, abdominal cramps; and 1, bloody stools. There were no deaths or hospitalizations.

A questionnaire was administered to all 92 guests and staff to ascertain risk factors for gastroenteritis. Guests consisted of unrelated groups, and they stayed in 18 separate cabins. All 36 of the patients and 37 of the 56 unaffected attendees had drunk water at their cabin. A dose-response relationship was demonstrated between the amount of water consumed and the attack rate. No illness occurred among the persons who did not drink water; 33% of those drinking 1-2 cups and 59% of those drinking >3 cups became ill. Five of the 18 cabins were unaffected; three of these belonged to families who were residents or frequent visitors at the lodge.

Assuming guests were exposed upon arrival or when they first drank water, the median incubation period was 41 hours (range 7-110 hours). Symptoms lasted from 2-17 days, with a median of 5 days.

The cabins were supplied with water taken from a stream and processed through a small chlorinator and a storage tank that was periodically iodized. A filter had been removed recently from the pipe because it repeatedly became plugged with debris. A severe rainstorm occurred the evening the guests arrived, resulting in increased water turbidity.

Water samples taken at the cabins and the surface stream that supplied the cabins were positive for total coliforms and fecal coliforms. Stool samples from ill patrons were negative for pathogenic bacteria and parasites, except for one sample, from which Giardia was isolated. Convalescent-phase sera were submitted to CDC for 13 cases and 26 controls (2 per case), matched for age within 5 years, gender, and city of residence. Controls were selected from health department personnel who had not visited the lodge. No difference in Norwalk titers was found between five cases and five controls.

Under the supervision of state environmentalists, the water system was renovated before the lodge reopened, with particular emphasis on filters, the chlorinator, and the storage tank. Reported by: PA Bonrud, MS, AL Volmer, TL Dosch, W Chalcraft, D Johnson, B Hoon, M Baker, KA Senger, State Epidemiologist, South Dakota State Dept of Health. CF Martinez, TO Madrid, MPA, RM Gallegos, MS, SP Castle, MPH, CM Powers, JA Knott, RM Gurule, MS Blanch, LJ Nims, MS, PW Gray, PA Gutierrez, MS, M Eidson, DVM, MV Tanuz, HF Hull, MD, State Epidemiologist, New Mexico Health and Environment Dept. Respiratory and Enteroviral Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

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