Epidemiologic field investigations by the Centers for Disease control and Epidemic Intelligence Service, 1946-87.

The epidemiologic field investigation is an important tool used by the Centers for Disease Control (CDC) to provide assistance to State, local, and international public health agencies. The Epidemic Intelligence Service (EIS) of the CDC is an ongoing program that gives physicians and other health professionals opportunities to learn and practice epidemiology. In the period 1946-87, EIS Officers and other professional staff based at CDC headquarters participated in 2,900 epidemiologic field investigations requested by State, local, and international public health agencies. Nearly two-thirds of the investigations involved infectious disease problems, while 13 percent involved noninfectious conditions; for 21.1 percent, the etiology of the problem was unknown when the investigation was initiated. Among the specific subcategories, bacterial causes were the most common, accounting for 864 (29.8 percent) of all investigations. During this 41-year period, an increasing proportion of the field epidemiologic investigations involved public health problems of noninfectious etiology. Trends in the types of investigations done probably represent the influence of such factors as CDC's priorities, organizational structure, and budget; the size of the EIS Program; national health initiatives; and the States' needs and programs.

Paralytic poliomyelitis can be eliminated.

Since the introduction and widespread use of inactivated and oral poliovirus vaccines, there has been a continued and increasing commitment to worldwide poliomyelitis control. The eradication of poliomyelitis in certain countries, smallpox eradication worldwide, the World Health Organization's (WHO) Expanded Programme on Immunization, and advances in poliovirus vaccine production augur well for worldwide elimination within the next few decades. The success of any such program rests firmly upon scientific feasibility, intensive epidemiologic surveillance, and economic justification. The development of a variety of disease-specific control/prevention programs worldwide have improved communicable disease reporting in many countries and established health-care infrastructure as well. Equally important has been the emergence of the concept of epidemiologic surveillance. The success of poliomyelitis elimination in large parts of the world, the WHO commitment, and the tragic, visible effects of poliomyelitis are sufficiently strong arguments to persuade the countries of the world to make the necessary effort to eliminate poliomyelitis within the next generation.

Pontiac fever: isolation of the etiologic agent (Legionella pneumophilia) and demonstration of its mode of transmission.

Pontiac fever, a unique epidemiologic form of legionellosis, is characterized by a short (one- to two-day) incubation period and a self-limited grippe-like illness without pneumonia. In 1968, the first documented outbreak of this syndrome affected persons who had entered a health department building in Pontiac, Michigan. Epidemiologic analyses clearly implicated as airborne agent and suggested that evaporative condenser water aerosols being disseminated by a defective air conditioning system played a key role in the outbreak. Guinea pigs that were exposed in the building and to laboratory aerosols of evaporative condenser water developed bronchopneumonia. Legionella pneumophilia (serogroup 1) was isolated from the exposed guinea pigs' lungs. Paired acute and convalescent serum specimens from 37 patients were tested by the indirect fluorescent antibody technique using L. pneumophila serogroup 1 antigen, and 31 (84%) had rises in titer from less than 32 to greater than or equal to 64.

The Russian flu. Its history and implications for this year's influenza season.

From November 1977 through mid-January 1978 the population younger than 25 years in the Union of Soviet Socialist Republics experienced a widespread epidemic of mild influenza (Russian flu) caused by an H1N1 virus similar to the virus that circulated worldwide during the early 1950s. Outbreaks of Russian flu occurred in school populations and military recruits in the United States starting in mid-January. Many other countries reported outbreaks of H1N1 virus in the winter of 1978. Predictions of influenza activity are always hazardous, but most experts believe that the Russian flu may occur again in the fall and winter of 1978. Other type A and B strains may also circulate; therefore, a trivalent vaccine containing A/USSR, A/Texas, and B/Hong Kong virus strains will be available. It is recommended that the chronically ill and those 65 years and older be the target populations for annual vaccination.

Pontiac fever. An epidemic of unknown etiology in a health department: I. Clinical and epidemiologic aspects.

In July 1968, an explosive epidemic of acute febrile illness occurred at a county health department facility in Pontiac, Michigan. Illness characterized principally by fever, headache, myalgia, and malaise affected at least 144 persons, including 95 of 100 persons employed in the health department building. The mean incubation period was approximately 36 hours. Illness was self-limited, generally lasting from two to five days. Secondary cases did not occur in family contacts and second attacks did not consistently follow re-exposure in the building. A defective air-conditioning system was implicated as the source and mechanism of spread of the causative factor. However, extensive laboratory and environmental investigations failed to identify the etiologic agent. Since these investigations a bacterium similar to or identical with the agent responsible for Legionnaires' Disease has been isolated from guinea pigs exposed to the Pontiac health department building in 1968 as well as from guinea pigs exposed to water from the evaporative condenser. Paired sera from 32 cases of Pontiac Fever showed seroconversion or diagnostic rises in antibody titers to this bacterium.

Diagnostic criteria for influenza B-associated Reye's syndrome: clinical vs. pathologic criteria.

Between December 15, 1973, and Jun 30, 1974, a total of 379 cases of Reye's syndrome was reported to the Center for Disease Control. One hundred forty-seven (40%) were confirmed by either autopsy or biopsy, while 232 were diagnosed by clinical and laboratory parameters. Comparisons of the epidemiologic and demographic characteristics, the hospital course, the outcome, and the laboratory abnormalities of the clinically diagnosed and the pathologically confirmed cases revealed no significant differences. In the epidemiologic setting of influenza B outbreaks, children who have the acute onset of noninflammatory encephalopathy associated with elevated serum transaminase levels, hypoprothrombinemia, and elevated blood ammonia levels should be considered to have Reye's syndrome. Further evaluation of diagnostic criteria is needed, however, for sporadically occurring, nonepidemic cases of noninflammatory encephalopathy associated with hepatic dysfunction.

Influenza B-associated Reye's syndrome: incidence in Michigan and potential for prevention.

Prospective surveillance for Reye's syndrome in Michigan revealed the occurrence of 46 cases between December 15, 1973 and June 1, 1974. In an attempt to determine the incidence of influenza B-associated Reye's syndrome, a randomized point-prevalence survey of 1,041 schoolchildren was done in a county in Michigan where there had been simultaneous outbreaks of influenza B and Reye's syndrome. Of the children tested, 20% had titers of hemagglutination-inhibiting antibody to influenza virus B/Hong Kong/5/72 of greater than or equal 1:20. Based upon this countywide survey, the incidence of Reye's syndrome following influenza B was estimated as between 30.8 and 57.8 cases of Reye's syndrome per 100,000 cases of influenza B. A detailed epidemiologic investigation of the patients who developed Reye's syndrome indicated that the syndrome occurred four times more frequently in children living in rural areas than in children in the urban areas of the state. These studies indicate that, in addition to antecedent viral infections such as influenza B, factor(s) that are most likely extrinsic or environmental also play a role in the pathogenesis of Reye's syndrome.

Transmission of hepatitis B associated with hemodialysis: role of malfunction (blood leaks) in dialysis machines.

In the first 10 months of 1974, 26 of 60 susceptible patients in a commercial hemodialysis unit developed asymptomatic infection with hepatitis B virus; 17 (65%) of the 26 cases occurred in 14 weeks from July to October. In a case-control study, 15 of 16 cases for whom records were available were found to be associated with malfunctions of dialysis machines (primarily leaks or ruptures in dialysis membranes) that had occurred before patients converted to hepatitis B surface antigen (HBs Ag) positivity. In comparison, 17 of 34 controls were associated with machine malfunctions (P less than 0.01). In addition, the mean number of malfunctions in machines per patient was significantly greater for cases of infection (2.25 +/- 1.34) than for controls (1.06 +/- 1.39) (P less than 0.01). Furthermore, a direct correlation was demonstrated between an increase in blood leaks in machines used with susceptible patients and subsequent increases in cases of hepatitis for the various beds in the unit (r=0.994, P less than 0.0001). The mean period from the last blood leak to HBs Ag seroconversion was 67 days. Six of the 36 blood leaks associated with cases of infection occurred less than 6 hr after leaks in the contaminated area, whereas only one of 36 leaks associated with controls demonstrated this relationship (P less than 0.05). These data suggest that the conversion to HBs Ag positivity was linked to the occurrence of machine malfunctions (blood leaks) and that events which occurred during these episodes caused the spread of infection.

Hemodialysis-associated hepatitis: report of an epidemic with further evidence on mechanisms of transmission.

In the period January-September 1974, 50 cases of hepatitis B infection occurred among a nephrology center's hemodialysis patients and staff. The in-center patient population had an attack rate of 96%. Epidemiologic analysis of risk factors for patients revealed an association between the receipt of intravenous medication and the subsequent development of hepatitis, suggesting that parenteral inoculation was a mode of spread among patients (p equals .008). Nineteen per cent of the staff contracted hepatitis, and all of these personnel had had close contact with patients (p equals .005). The prevalence of hepatitis B infection in staff was related to the failure to use gloves (p less than .01), and accidental needle puncture was associated with the development of clinical hepatitis. These data suggested that disease was transmitted to staff by contact with contaminated blood or close personal contact with patients. Additional data showed that the presence of endogenous antibody protected both patients and staff from antigenemia (p equals .002). These data support the hypothesis that contact with blood is the primary mechanism of spread of hepatitis B in dialysis units, and suggest that, as preventive measures, gloves should be used and antibody-positive staff should dialyze antigen-positive patients.

Vaccine-associated poliomyelitis in the United States, 1961-1972.

Although poliovirus vaccines have led to a dramatic reduction in the incidence of poliomyelitis in the United States, there is evidence that vaccine-related cases have occurred in both vaccine recipients (recipient cases) and their contacts (contact cases) and that the incidence and epidemiologic characteristics of these cases in the 12-year period 1961-1972 have changed. Before 1965, there were 63 recipient cases compared with only 16 between 1965 and 1972. These latter cases were in younger persons and were more frequently associated with trivalent oral poliovirus vaccine (TOPV) than the former cases. Both groups were predominantly male and had intervals between immunization and onset of illness that clustered between 7 and 21 days. Only three contact cases were recognized before 1965, compared with 39 cases in 1965-1972. The increase was in both children and adults. Unlike recipient cases, contact cases were almost as frequent in females as in males. Evidence that the contact cases were vaccine-related included the apparent clustering between 20 and 29 days of the intervals from vaccine administration to onset of illness and the significantly increased frequency of longer intervals for contact cases in non-household members compared with contact cases in household members. The decrease in recipient cases and the increase in contact cases in 1965-1972 compared with the previous 3-year period are explained by the general curtailing of routine vaccination of adults after 1964, a switch from monovalent oral polio vaccine to TOPV, improved recognition of contact cases and a shift in emphasis from mass vaccination campaigns and communitywide programs to routine vaccination of infants.

Live, attenuated influenza A/England/42/72 (H3N2) virus vaccine: a field trial.

Two doses of a live, attentuated influenza A/England/42/72 (H3N2) vaccine virus (inhibitor-insensitive Alice strain) were administered intranasally to 130 university students, and placebo was given to 134 students. Fourfold or greater rises in titer of hemagglutination-inhibiting antibody occurred in 68% of all vaccine recipients and in 88% of those with initial titers of less than 1:8; the geometric mean titer of hemagglutination-inhibiting antibody increased from 1:15 to 1:77. A 3.2-fold rise in titer of neuraminidase-inhibiting antibody occurred in 24% of the students. Side effects produced by administration of the vaccine include mild rhinitis and sore throat, which were found only during the first four days after administration of the first dose. Inhibitor-insensitive virus was shed only by three of 31 intensively studied vaccine recipients; these three subjects all had initial serum titers of hemagglutination-inhibiting antibody of less than 1:8. No transmission of vaccine virus to spouses was detected. During a 12-month interval after vaccination, the geometric mean titer of hemagglutination-inhibiting antibody in serum and the prevalence of antibody decreased minimally among the 47 vaccine recipients still available for study.

Clinical aspects of human Venezuelan equine encephalitis in Texas.

The Venezuelan equine encephalitis epidemic which occurred in Texas in 1971 produced a wide range of predominantly mild clinical symptoms. This epidemic, which peaked on 13-14 July, was most intensely felt in the far-south counties of Cameron and Hidalgo. In all, 88 laboratory-confirmed human cases were reported to the U.S. Center for Disease Control by the Texas State Department of Health. The ratio of male to female cases was about two to one. An attack of 20.8 cases per 100,000, observed in both the 20-29 and 30-39 age groups, was higher than attack rates experienced by other age groups and by the population at large. Together, Cameron and Hidalgo counties experienced a much higher overall attack rate (21.7 cases por 100,000) than did affected counties in the Corpus Christi area (4.9 cases per 100,000). Knowledge about when various patients were first exposed points to an incubation period ranging from 27.5 hours to four days. In those 79 cases for which clinical data were available, the most common clinical manifestations were found to be fever, severe headache, myalgia, and chills. Evidence of mild to moderate central nervous system involvement was found in 10 out of 25 children and young people under 17 years of age, and in six out of 54 adults. Two children still had residual paralysis six weeks after onset of illness, but by 10 months these sequelae had disappeared. Seven of the 54 adults, however, still complained of tiring easily a year after onset of illness. Leukopenia, as demonstrated by a count of less rhan 4,500 white blood cells per cubic millimeter, was observed in 75 per cent of the patients examined.

Clinical aspects of human Venezuelan equine encephalitis in Texas

The Venezuelan equine encephalitis epidemic which occurred in Texas in 1971 produced a wide range of predominantly mild clinical symptoms. This epidemic, which peaked on 13-14 July, was most intensely felt in the far-south counties of Cameron and Hidalgo. In all, 88 laboratory-confirmed human cases were reported to the U.S. Center for Disease Control by the Texas State Department of Health. The ratio of male to female cases was about two to one. An attack of 20.8 cases per 100,000, observed in both the 20-29 and 30-39 age groups, was higher than attack rates experienced by other age groups and by the population at large. Together, Cameron and Hidalgo counties experienced a much higher overall attack rate (21.7 cases por 100,000) than did affected counties in the Corpus Christi area (4.9 cases per 100,000). Knowledge about when various patients were first exposed points to an incubation period ranging from 27.5 hours to four days. In those 79 cases for which clinical data were available, the most common clinical manifestations were found to be fever, severe headache, myalgia, and chills. Evidence of mild to moderate central nervous system involvement was found in 10 out of 25 children and young people under 17 years of age, and in six out of 54 adults. Two children still had residual paralysis six weeks after onset of illness, but by 10 months these sequelae had disappeared. Seven of the 54 adults, however, still complained of tiring easily a year after onset of illness. Leukopenia, as demonstrated by a count of less rhan 4,500 white blood cells per cubic millimeter, was observed in 75 per cent of the patients examined (Au)

Clinical aspects of human Venezuelan equine encephalitis in Texas

The Venezuelan equine encephalitis epidemic which occurred in Texas in 1971 produced a wide range of predominantly mild clinical symptoms. This epidemic, which peaked on 13-14 July, was most intensely felt in the far-south counties of Cameron and Hidalgo. In all, 88 laboratory-confirmed human cases were reported to the U.S. Center for Disease Control by the Texas State Department of Health. The ratio of male to female cases was about two to one. An attack of 20.8 cases per 100,000, observed in both the 20-29 and 30-39 age groups, was higher than attack rates experienced by other age groups and by the population at large. Together, Cameron and Hidalgo counties experienced a much higher overall attack rate (21.7 cases por 100,000) than did affected counties in the Corpus Christi area (4.9 cases per 100,000). Knowledge about when various patients were first exposed points to an incubation period ranging from 27.5 hours to four days. In those 79 cases for which clinical data were available, the most common clinical manifestations were found to be fever, severe headache, myalgia, and chills. Evidence of mild to moderate central nervous system involvement was found in 10 out of 25 children and young people under 17 years of age, and in six out of 54 adults. Two children still had residual paralysis six weeks after onset of illness, but by 10 months these sequelae had disappeared. Seven of the 54 adults, however, still complained of tiring easily a year after onset of illness. Leukopenia, as demonstrated by a count of less rhan 4,500 white blood cells per cubic millimeter, was observed in 75 per cent of the patients examined (Au)