[Epidemiology of transmissible diseases. Surveillance methods, notification, research on an outbreak in a community and preventive measures].
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The paper presents the results of investigations of hepatitis E (HE), which have been made at the Department of Viral Hepatitides, M. P. Chumakov Institute of Poliomyelitis and Viral Encephalitides, Russian Academy of Medical Sciences. M. S. Balayan's discovery of hepatitis E virus permitted etiological interpretation of the cases of so-called non-A, non-B hepatitis with its fecal and oral transmission. The detection of antibodies to HE virus among different groups of the population of Russia (i.e. a hepatitis E nonendemic region of the world) suggests that they are frequently detected in the absence of disease notification. The fact that viral HE RNA has been detected in the pigs and wild boars inhabiting in the country is evidence in favor of an assumption that the virus is spread among these animals. The hypothesis for HE as a zoonosis is discussed in the paper.
Information from routine and sentinel surveillance was used to monitor the HIV/AIDS epidemic in KwaZulu-Natal, South Africa between 1991 and 1997. Comparisons were made between data obtained from (1) sentinel surveillance for antenatal HIV infection, pulmonary tuberculosis (PTB), and AIDS in a single health district and (2) province-wide sentinel surveillance for antenatal HIV infection, legally required notification of cases of PTB, and voluntary notification of AIDS cases. HIV prevalence among antenatal clinic attenders in the sentinel district rose rapidly and at similar rates to provincial figures: 4.2% vs 4.8% in 1992 to 25.9% vs 26.9% in 1997. PTB incidence increased four-fold in the sentinel district over the study period, whereas provincial PTB figures from passive surveillance fluctuated widely and showed no clear increase (Chi-square for trend 425.5, P<0.00001). AIDS incidence in the sentinel district increased dramatically while provincial data from the voluntary reporting system showed a less consistent and much slower rise (Chi-square for trend 9.07, P=0.003). Incidence of AIDS in 1997 was estimated as 437/10(5) in the sentinel district compared to 32/10(5) in the provincial figures. Routine disease notification and voluntary reporting systems are likely to underestimate the impact of the HIV/AIDS epidemic in resource-poor settings. Sentinel surveillance at representative sites should be developed to validate or replace passive surveillance systems.
The objective was to describe the current epidemiology and trends in New Zealand human leptospirosis, using descriptive epidemiology of laboratory surveillance and disease notification data, 1990-8. The annual incidence of human leptospirosis in New Zealand 1990-8 was 44 per 100,000. Incidence was highest among meat processing workers (163.5/100,000), livestock farm workers (91.7), and forestry-related workers (24.1). The most commonly detected serovars were Leptospira borgpetersenii serovar (sv.) hardjo (hardjobovis) (46.1%), L. interrogans sv. pomona (24.4%) and L. borgpetersenii sv. ballum (11.9%). The annual incidence of leptospirosis declined from 5.7/100,000 in 1990-2 to 2.9/100,000 in 1996-8. Incidence of L. borgpetersenii sv. hardjo and L. interrogans sv. pomona infection declined, while incidence of L. borgpetersenii sv. ballum infection increased. The incidence of human leptospirosis in New Zealand remains high for a temperate developed country. Increasing L. borgpetersenii sv. ballum case numbers suggest changing transmission patterns via direct or indirect exposure to contaminated surface water. Targeted and evaluated disease control programmes should be renewed.
The efficient execution of an occupational epidemiologic study requires accurate information on both exposure and effect. In this paper emphasis is placed on the use of registers of occupation or disease as tools in the undertaking of descriptive and analytical epidemiologic studies. While cancer registers are a common information source nowadays, their validity is not always consistently good. Other sources of information, such as industry records, professional membership listings, and disease notifications are also used. The inaccuracies of these registers--established usually for nonepidemiologic purposes--are outlined. Specific examples are used to illustrate the problems and pitfalls involved in interpreting the derived results. The study populations discussed range from the high enumeration feasible with life-long occupational groupings, such as pathologists and sea pilots, to attempts to trace individuals whose "membership" in an exposure group might be residence in the American Embassy in Moscow or recognition as short-service military personnel exposed to A-bomb testing a generation ago. The recent development of using census-based occupational information to trace mortality and morbidity is also discussed.
A nationwide outbreak of Lancefield group A streptococcal (GAS) infections in Norway during the season 1987-88 is described. Data were collected from the Norwegian infectious disease notification system and supplemented by active search for cases of bacteraemia and other serious infections in addition to serotyping of selected clinical bacterial isolates. The number of reported cases of non-invasive GAS infections from week 29/1987 to week 28/1988 was 60% higher than expected. Between 1 Jan. and 30 June 1988, 84 cases of bacteraemia were notified, several with fulminant septicaemia and shock. The case fatality rate was 25%. Six cases of neonatal GAS septicaemia were seen. There was a nearly 3-fold total increase in occurrence of GAS bacteraemia compared with previous years, and the increase was marked particularly in cases among older children and adults 30-50 years old. Additional culture-confirmed diagnoses included unusual cases compared to recent decades such as pneumonia with empyema, necrotising fasciitis and primary peritonitis. Serotyping of strains collected consecutively from localized infections revealed a marked predominance of T-type 1, opacity factor negative strains (T-1 OF-), ranging from 41% in North Norway to 87% in Mid-Norway. M-typing confirmed that these strains were M-1, as were 87% of the preserved bacteraemia strains from the period described. Although most of the M-1 strains were distinctly mucoid only one case of acute rheumatic fever was reported during the first half of 1988. We conclude that an epidemic of GAS infections caused by M-1 strains has occurred in Norway resulting in an increase in both incidence and seriousness of disease.
OBJECTIVE: To investigate trends in AIDS mortality and incidence in Brazil over the period of 1984 to 2000 and to assess the impact of the introduction of universal access to highly active antiretroviral therapy (HAART) in the country in 1996. METHODS: Data from the Brazilian disease notification system and the national mortality information system were used to calculate annual region-specific and sex-specific AIDS incidence and mortality rates. We also calculated sex- and region-specific ratios of the number of AIDS deaths in one year to the number of AIDS cases notified two years earlier. RESULTS: AIDS mortality rates for both men and women and in all five of the geographic regions of Brazil declined following introduction of HAART, despite continued growth in AIDS incidence. The ratio of the number of AIDS deaths in one year to the number of AIDS cases notified two years earlier for men equalized rapidly with the ratio for women following introduction of HAART. More recently, AIDS incidence declined for both sexes and in most of the regions of Brazil. CONCLUSIONS: Despite Brazil's resource limitations and disparities in wealth between men and women and among the country's regions, the introduction of universal access to HAART in Brazil has helped achieve impressive declines in AIDS mortality, and it may also be contributing to declines in AIDS incidence.
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Statistical time series models are practical tools in public health surveillance. Their capacity to forecast future disease incidence values exemplifies their usefulness. Using these forecasts, one can develop strategies to trigger alerts to public health officials when irregular disease incidence values have occurred. Clearly, the better the forecasting performance of the model class used in the time series analysis, the more realistic are the alerts triggered. The time series analysis of disease incidence values has often entailed the Box and Jenkins model class. However, this class was designed to model real-valued variables whereas disease incidences are integer-valued variables. A new class of time series models, called integer-valued autoregressive models, has been developed and studied over the past decade. The objective of this paper is to introduce this new class of models to the application of time series analysis of infectious disease incidence, and to demonstrate its advantages over the class of real-valued Box and Jenkins models. The paper also presents a bootstrap method developed for the calculation of forecast interval limits.
We model an outbreak of acute haemorrhagic conjunctivitis (AHC) using a simple epidemic model that includes susceptible, infectious, reported, and recovered classes. The model's framework considers the impact of underreporting and behaviour changes on the transmission rate and is applied to a recent epidemic of AHC in Mexico, using a fit to the cumulative number of cases to estimate model parameters, which agree with those derived from clinical studies. The model predicts a 'mean time from symptomatic onset to diagnosis' of 1.43 days (95 per cent CI: 1-2.5) and that the final size of the Mexican epidemic was underreported by 39 per cent. We estimate that a primary infectious case generates approximately 3 secondary cases (R0* = 2.64, SD 0.65). We explore the impact of interventions on the final epidemic size, and estimate a 36 per cent reduction in the transmission rate due to behaviour changes. The effectiveness of the behaviour changes in slowing the epidemic is evident at 21.90 (SD 0.19) days after the first reported case. Results therefore support current public health policy including expeditious announcement of the outbreak and public health information press releases that instruct individuals on avoiding contagion and encourage them to seek diagnosis in hospital clinics.
The paper presents an application of back-projection methods to the reported AIDS data which are collected by the AIDS Center in the Federal Office of Health, Berlin. The analysis is based on all data reported up to 31 December 1992. The data are broken down by major risk groups. Correction for reporting delays takes into account temporal changes in their distribution. The paper applies the EMS algorithm for the estimation of HIV incidence. The incubation period is modelled according to a convolution of several exponential distributions which describe time dependent phenomena like change of case definition and therapy effects. For each case it is reported whether an antibody test has been performed before diagnosis, and if yes, at what time this test was performed. The modelling of the incubation distribution takes into account the transition from a state 'not yet tested' into a state 'tested'. Only tested individuals in three pre-AIDS states are eligible for treatment. The model allows us to estimate not only the current total HIV prevalence but also a breakdown into those that are not yet tested, those that are tested but not yet treated and those that are under treatment. The results depend on the assumptions about the effect of treatment and on the degree of smoothing applied in the EMS algorithm.
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Several health plans and other organizations are collaborating with the Centers for Disease Control and Prevention to develop a syndromic surveillance system with national coverage that includes more than 20 million people. A principal design feature of this system is reliance on daily reporting of counts of individuals with syndromes of interest in specified geographic regions rather than reporting of individual encounter-level information. On request from public health agencies, health plans and telephone triage services provide additional information regarding individuals who are part of apparent clusters of illness. This reporting framework has several advantages, including less sharing of protected health information, less risk that confidential information will be distributed inappropriately, the prospect of better public acceptance, greater acceptance by health plans, and less effort and cost for both health plans and public health agencies. If successful, this system will allow any organization with appropriate data to contribute vital information to public health syndromic surveillance systems while preserving individuals' privacy to the greatest extent possible.
This article presents an algorithm for performing early detection of disease outbreaks by searching a database of emergency department cases for anomalous patterns. Traditional techniques for anomaly detection are unsatisfactory for this problem because they identify individual data points that are rare due to particular combinations of features. Thus, these traditional algorithms discover isolated outliers of particularly strange events, such as someone accidentally shooting their ear, that are not indicative of a new outbreak. Instead, we would like to detect groups with specific characteristics that have a recent pattern of illness that is anomalous relative to historical patterns. We propose using an anomaly detection algorithm that would characterize each anomalous pattern with a rule. The significance of each rule would be carefully evaluated using the Fisher exact test and a randomization test. In this study, we compared our algorithm with a standard detection algorithm by measuring the number of false positives and the timeliness of detection. Simulated data, produced by a simulator that creates the effects of an epidemic on a city, were used for evaluation. The results indicate that our algorithm has significantly better detection times for common significance thresholds while having a slightly higher false positive rate.
After the 2001 World Trade Center disaster, the New York City Department of Health was under heightened alert for bioterrorist attacks in the city. An emergency department (ED) syndromic surveillance system was implemented with the assistance of the Centers for Disease Control and Prevention to ensure early recognition of an increase or clustering of disease syndromes that might represent a disease outbreak, whether natural or intentional. The surveillance system was based on data collected 7 days a week at area EDs. Data collected were translated into syndromes, entered into an electronic database, and analyzed for aberrations in space and time within 24 hours. From September 14-27, personnel were stationed at 15 EDs on a 24-hour basis (first staffing period); from September 29-October 12, due to resource limitations, personnel were stationed at 12 EDs on an 18-hour basis (second staffing period). A standardized form was used to obtain demographic information and classify each patient visit into 12 syndrome categories. Seven of these represented early manifestations of bioterrorist agents. Data transfer and analysis for time and space clustering (alarms) by syndrome and age occurred daily. Retrospective analyses examined syndrome trends, differences in reporting between staffing periods, and the staff's experience during the project. A total of 67,536 reports were received. The system captured 83.9% of patient visits during the first staffing period, and 60.8% during the second staffing period (P < 0.01). Five syndromes each accounted for more than 1% of visits: trauma, asthma, gastrointestinal illness, upper/lower respiratory infection with fever, and anxiety. Citywide temporal alarms occurred eight times for three of the major bioterrorism-related syndromes. Spatial clustering alarms occurred 16 times by hospital location and 9 times by ZIP code for the same three syndromes. No outbreaks were detected. On-site staffing to facilitate data collection and entry, supported by daily analysis of ED visits, is a feasible short-term approach to syndromic surveillance during high-profile events. The resources required to operate such a system, however, cannot be sustained for the long term. This system was changed to an electronic-based ED syndromic system using triage log data that remains in operation.
The Syndromic Surveillance Information Collection (SSIC) system aims to facilitate early detection of bioterrorism attacks (with such agents as anthrax, brucellosis, plague, Q fever, tularemia, smallpox, viral encephalitides, hemorrhagic fever, botulism toxins, staphylococcal enterotoxin B, etc.) and early detection of naturally occurring disease outbreaks, including large foodborne disease outbreaks, emerging infections, and pandemic influenza. This is accomplished using automated data collection of visit-level discharge diagnoses from heterogeneous clinical information systems, integrating those data into a common XML (Extensible Markup Language) form, and monitoring the results to detect unusual patterns of illness in the population. The system, operational since January 2001, collects, integrates, and displays data from three emergency department and urgent care (ED/UC) departments and nine primary care clinics by automatically mining data from the information systems of those facilities. With continued development, this system will constitute the foundation of a population-based surveillance system that will facilitate targeted investigation of clinical syndromes under surveillance and allow early detection of unusual clusters of illness compatible with bioterrorism or disease outbreaks.
Since 1995, the German Federal Ministry for Health and Social Security funds National Reference Centres (NRC) for the laboratory surveillance of important pathogens and syndromes. Which pathogens or syndromes are selected to be covered by a NRC depends on their epidemiological relevance, the special diagnostic tools, problems with antimicrobial resistance and necessary infection control measures. Currently, there are 15 NRC, which are appointed for a period of 3 years (currently from January 2005 through December 2007). Towards the end of their appointment all NRC are evaluated by a group of specialists. The assessment of their achievements is guided by a catalogue of tasks for the NRC. In addition to the NRC, a total of 50 laboratories are appointed which provide specialist expertise for additional pathogens in order to have a broad range of pathogens for which specialist laboratories are available. Their predominant task is to give advice and support for special diagnostic problems. Both NRC and the specialist laboratories are important parts of the network for infectious disease epidemiology.
The epidemiology of infectious foodborne diseases has changed. Outbreaks more frequently occur geographically dispersed or protractedly over longer periods of time, and they often appear as a scatter of seemingly sporadic cases. This hampers and delays the identification of their epidemiological link. The surveillance of infectious foodborne diseases has to be refined accordingly to be able to detect these diffuse outbreaks. The German Protection against Infection Act, enacted in 2001, offers the potential of increased sensitivity due to timely electronic reporting of individual cases and detailed data accompanying each report. In addition to a timely and comprehensive reporting system, subtyping of pathogens has become an invaluable tool in identifying epidemiologically linked cases, i.e. outbreaks. Still, the sensitivity of foodborne disease surveillance still hinges on the willingness of physicians to order stool testing for enteric pathogens (and to report suspected outbreaks to local health departments). Without the active participation of physicians, the chance of detecting outbreaks and successfully investigating them is markedly reduced. Consequently, the general preventive strategy would be jeopardised, namely to understand the (often new) mechanisms by which contamination and disease transmission occur well enough to interrupt them.