The main goal of the paper is to estimate efficiency of the modernized system of epidemiological surveillance for influenza during the 2009-2010 epidemic season. All cases of influenza, influenza-like diseases (ILD) and severe acute respiratory infection (SARI) were registered daily. Selective samples from patients with ILD and SARI were examined by PCR for the new A(H1N1)pdm influenza virus and the avian influenza virus A (H5N1).
The results of epidemiological surveillance during the 2009-2010 epidemic season showed an increased incidence of influenza and ILD in November and December. The peak morbidity was reached in November (week 47). SARI patients constituted 0.8% of the total number of influenza and ILD patients during the epidemic period. Also, an increased proportion of adults was registered among these patients.
Consequently, some measures were suggested to modernize the system of epidemiological surveillance for influenza in Uzbekistan and to optimize efficiency.
Influenza is still viewed as a major healthcare problem in nearly all countries of the world. It causes annual epidemics during which 5-15% of the global population gets infected. According to various estimates, from 3 to 5 million people suffer from a severe form of the disease and from 250,000 to 500,000 people die from influenza every year .
Occasionally, new highly pathogenic respiratory infections, such as atypical pneumonia, avian influenza A(H5N1) or the new pandemic (H1N1) 2009 influenza, appear . The provision of sophisticated epidemiological surveillance is essential when faced with emerging infections. An effective epidemiological surveillance system may be helpful in determining measures against seasonal influenza and may also contribute to the pandemic preparedness and control over new respiratory infections [3, 4].
Full-scale sophisticated surveillance over influenza and influenza-like diseases (ILD), acute respiratory infections (ARI) and severe acute respiratory infections (SARI) yields the most precise estimate of the epidemiological situation. In addition, the surveillance enables accurate prediction of disease incidence dynamics that is necessary to design the most appropriate plan of anti-epidemic measures and to organize the most effective preventive intervention .
This study examined the existing state of the epidemiological surveillance over influenza in Uzbekistan and the modernization of the system with regard to the current situation.
Due to the global epidemiological situation of influenza, a special Research and Policy Centre was established at the Institute of Virology in Uzbekistan to deal with the problems of seasonal influenza and avian influenza in the healthcare system. The system used for registering cases of influenza and ARI in the practical healthcare system was checked and its efficiency was analyzed. Within the system, all laboratory confirmed cases of influenza and all clinically diagnosed ARI cases of the upper respiratory tract were registered. No records on patients with ARI of the lower respiratory tract and with SARI were made in the system. There were no standard criteria for identifying nosological forms of respiratory tract diseases to be registered in the epidemiological surveillance system. This resulted in low quality and inadequate data that failed to satisfy the needs of the modern epidemiological surveillance system when faced with the possible spread of the A(H5N1) influenza virus, other SARIs and the risk of influenza pandemics.
To estimate the efficiency of the registration procedure for cases of acute respiratory infections in the epidemiological surveillance system, a retrospective analysis of medical records from 570 patients who visited 4 major out-patient clinics during the 2006-2007 epidemic season and who were diagnosed with various acute infections of the upper and lower respiratory tract was conducted. From August till December 2009, samples obtained from patients coming from other countries and suffering from SARI, ILD, and ARI were examined for the new A(H1N1)pdm influenza virus by the polymerase chain reaction (PCR) method. SARI and ILD patients suspected of having avian influenza because they met some clinical and epidemiological criteria for the disease were examined for influenza A(H5N1) by PCR.
The disease incidence was estimated by the intensity rate (number of cases of the disease per 100,000 population). Due to the small share of influenza and ILDs among the cases, the total incidence of influenza, ILD and ARI was analyzed. The incidence data for influenza (laboratory-confirmed cases), ILD (clinically diagnosed cases) and ARI (clinically diagnosed cases) were reported weekly to EuroFlu, epidemiological surveillance programme for influenza, for estimation of influenza activity in the WHO European region during the 2009-2010 epidemic season . The improved system of epidemiological surveillance was used for the first time to analyse the epidemiological situation in Uzbekistan during the pandemic (H1N1) 2009 influenza in 2009-2010.
The medical records for 570 cases of acute respiratory diseases were analysed. The clinical diagnosis (for example, “catarrh of the upper respiratory tract”) did not correspond to the list of acute respiratory infections compiled by the International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) for 37.2% of the cases . These cases were not classified as ARI in the health institutions and consequently were not reported and registered in the epidemiological surveillance system. In 16.5% of the cases a disease that did not correspond to the criteria of acute infection was registered as ARI.
The epidemiological surveillance modernization concept is included in the National Programme for Control over Influenza and Preparation for Pandemics in the Republic of Uzbekistan and the State Programme for Prevention of Epidemics, Epizootics and Epiphytes in the Republic of Uzbekistan . This concept also formed a basis for regulations for medical and preventive treatment facilities in the country.
ICD-10 off ers a more standardized list of clinical diagnoses of acute respiratory diseases of the upper and lower respiratory tract that are registered as ARI in the epidemiological surveillance system. In accordance with the new concept, all cases of laboratory-confirmed influenza, clinically diagnosed ILD and ARI of the upper and lower respiratory tract as well as SARI cases are registered. SARI cases need to be reported because they are important for current statistics and may indicate a need for adjusting routines at health institutions. In addition, SARI may be used as an indicator disease that demonstrates the spread of the A(H5N1) avian influenza and other highly pathogenic respiratory infections.
A special document was designed to unify the procedure of registering patients. The document covers all disease groups that are subject to epidemiological surveillance and provides a standard for the identification of a case to be registered. It includes a list of nosological forms of respiratory diseases to be registered in the epidemiological surveillance system as well as a description of standard criteria for clinical and epidemiological diagnostics.
Epidemiological investigations and laboratory analyses are performed for all diagnosed cases of SARI. If it is revealed that a patient has been in contact with birds, a joint epizootological and epidemiological investigation is organized in cooperation with veterinary specialists. Laboratory analysis for the A(H5N1) avian influenza virus by PCR is performed. The epidemiological and epizootological surveillance systems are supposed to exchange data regularly with the veterinary service that provides control over poultry in the private sector and poultry enterprises, and the wildlife protection service that provides control over wild birds. No cases of the A(H5N1) influenza were found among people or birds during the last 4 years.
For more intensive monitoring of the epidemiological situation, data on the number of patients diagnosed in healthcare institutions are reported daily to the state sanitary and epidemiological surveillance regional centres. The updated weekly data and the amended monthly reports on disease incidence are analyzed at the Research and policy centre and the results are used to adjust preventive and control measures.
The modernized surveillance system is comprised of two basic elements:
- Registration of all cases of the disease diagnosed in all healthcare institutions without laboratory analysis of samples.
- Sentinel surveillance of 2 or 3 healthcare institutions in 6 large cities located in different parts of the country, with laboratory analysis performed on samples from selected groups of patients.
From August to November 2009, 126 patients were examined for the new pandemic (H1N1) 2009 influenza. In the beginning of November (week 45) a laboratory confirmation for the (H1N1) 2009 influenza was received for only 2 patients. Three additional patients were diagnosed later by laboratory analyses. A total of 5 cases of the (H1N1) 2009 influenza were detected.
The improved system of epidemiological surveillance started to function in August 2009. The results of influenza, ILD and ARI surveillance during the 2009-2010 epidemic season demonstrated an epidemic growth in disease morbidity during November and December. In week 43, the ILD and ARI incidence exceeded the epidemic threshold by 14.3%. The highest incidence was registered in November in week 47 (Figure 1). The epidemic period lasted 14 weeks. As compared to the epidemic seasons of 2007-2008 and 2008-2009, in 2009 the seasonal growth of disease morbidity started earlier than usual and was more intensive than before. At its peak, the disease incidence was 2.7-3.0 times higher than in the same period of the previous years. In the second half of the season the intensity of the epidemic rapidly decreased. Although the total incidence for the entire 2009-2010 season was only 1.2-1.3 times higher than in the same period of the previous years, during weeks 46-48 the rate was 2.3-2.5 times higher than before.
Patients with SARI constituted 0.8% of the total number of patients suffering from influenza and ILD during the epidemic period. The SARI incidence grew rapidly in week 46. The maximum number of SARI cases was registered in week 53, the last week of 2009 (Figure 2).
The proportion of adults among the total number of patients increased during the 2009-2010 epidemic season. In October there were twice as many children as adults diagnosed but by December the ratio was already 1:1.5. According to EuroFlu estimates, the epidemic activity of influenza in Uzbekistan during the 2009-2010 epidemic season was low.
Fig. 2. Incidence of severe acute respiratory infections in epidemic season 2009-10 in Uzbekistan
The study showed that the previously applied method of the influenza incidence registration was inaccurate. In addition, the method did not provide adequate information for dealing with the challenges encountered by the healthcare system when the emergence of new highly pathogenic respiratory infections is probable. Due to the global epidemiological situation of A(H5N1) avian influenza and the probability of new influenza pandemics, a modernized system of epidemiological surveillance was designed and implemented in accordance with WHO recommendations. To achieve this goal, a special Research and Policy Centre was established. This centre defined the major areas for modernization of the epidemiological surveillance system. A list of nosological forms of respiratory diseases was compiled and standard epidemiological criteria for diagnostics, registration and reporting in the epidemiological surveillance system were determined. ARI of the lower respiratory tract and SARI were added to the list of diseases included in the epidemiological surveillance system. The weekly monitoring of disease morbidity was performed throughout the year. An interdepartmental control system to detect the emergence of A(H5N1) avian influenza cases among people and birds was organized.
The results of epidemiological surveillance during the 2009-2010 epidemic season indicate that the modernization has been useful. The improved epidemiological surveillance system made it possible to determine when the epidemiological growth of influenza incidence started, to take timely preventive and control measures against the epidemic and to prepare health institutions for the inflow of patients. The circulation of the new A(H1N1)pdm influenza virus was detected in the country. The inclusion of SARI in the epidemiological surveillance system contributed to a more accurate estimation of the burden of influenza and the epidemic situation. Epidemiological surveillance data showed that despite a considerable decrease in the intensity of ILD and ARI morbidity in weeks 52-53, the incidence of SARI during this period started to grow. This made it necessary to continue preventive and control measures against the epidemic and to advise the healthcare service to provide more active detection and treatment of patients with the severe illness.
With a centralized information collection system it became possible for Uzbekistan to participate in the EuroFlu program and to compare the epidemic activity of influenza in the country during 2009-2010 epidemic season with other countries in Europe and Central Asia. The retrospective morbidity analysis showed that after standard definitions of disease cases were introduced into the practical healthcare process, the proportion of influenza among all cases of ARI increased by 5.8 times.
The improved surveillance system has provided promising perspectives and increased the capacity of data collection and information. This may help to plan and conduct preventive and control measures for influenza and other highly pathogenic respiratory infections, including the A(H5N1) avian flu, in a more effective manner and to estimate the efficiency of the measures implemented.
- Всемирная организация здравоохранения, 2009 (http://www.who.int/mediacentre/factsheets/fs211/ru/).
- Львов Д.К. Новые и вновь возникающие вирусные инфекции// Врач.- М., 2000.- №8.- С. 13-14.
- Европейское руководство ВОЗ по эпиднадзору за гриппом среди людей. - Копенгаген, 2009.
- Асадов Д.А. Стратегия реформ систем здравоохранения с позиции Всемирной организации здравоохранения// Медицинский журнал Узбекистана.- 2009; 3: 47-51.
- «Международная статистическая классификация болезней и проблем, связанных со здоровьем» , 10-й пересмотр,43-я Всемирная aссамблея здравоохранения, 1992 г.
- Государственная программа по предупреждению эпидемий, эпизоотий и эпифитотий на территории Республики Узбекистан. Мероприятия по профилактике и контролю за гриппом и подготовке к пандемии. -Ташкент, 2006, 141 с.
- http://www.eurofl u.org/cgi-fi les/bulletin