During the last decade, the epidemiological situation regarding meningococcal infection in the Republic of Komi in general and the City of Pechora in particular has remained tense but stable. The Republic of Komi has a mean rank distribution of meningococcal infection incidence . There were some sporadic foci of infection through direct contact registered mostly among children. No cluster cases were reported. In March 2009 a cluster of meningococcal infection including two lethal cases was registered among teenagers. Measures such as immunization of risk groups as well as the detection and isolation of infection sources have helped to limit the epidemic focus during the incubation period.
Meningococcal infection is an anthroponosis caused by Neisseria meningitidis. The infection has various clinical forms. Twelve serogroups are distinguished by the polysaccharide structure: А, В, С, Х, У, Z, W-135, 29Е, K, H, L and J. The meningococci of serogroups А, В and С are the most dangerous and can cause disease and outbreaks. The infection can be transmitted by patients suffering from the generalized form of meningococcal infection, from meningococcal nasopharyngitis and also by carriers of meningococci. The clinical manifestations of meningococcal infection vary including localized forms (e.g. nasopharyngitis) as well as generalized forms (e.g. meningitis, meningococcemia, combined forms, meningococcal pneumonia, endocarditis, arthritis and iridocyclitis). The transmission of the pathogen is by droplets. In most cases the infection is spread by asymptomatic carriers while transmission occurs less often through direct contact with a patient suffering from the generalized form of meningococcal infection. For children the risk of infection is higher than for adults. The infection has a high social and economic relevance because it can cause generalized forms of the disease that often require intensive care and may have severe outcomes. A range of activities target epidemic control and prevention in the infection focus.
Prevention of meningococcal infection is through immunization of the population in accordance with the vaccination schedule and in compliance with epidemic indications. Prophylactic immunization is necessary when an adverse epidemiological situation is indicated by increased disease morbidity and incidence rates among the population (over 20 cases per 100,000 population). Epidemiological surveillance of meningococcal infection is of major importance since it helps to reveal a worsening of the epidemiological situation as early as possible. Studies addressing immunity in indicator groups of young people attending educational institutions or at places of work are recommended to detect the circulation of meningococci.
The goal of this study is to examine and analyze the epidemiology of meningococcal infection in Pechora in order to plan and implement measures targeted at stabilizing and improving the epidemiological situation in this area.
Fig. 1. Meningococcal infection incidence in the Republic of Komi and the city of Pechora per 100,000 population (1980-2008)
The outbreak was investigated using descriptive epidemiological methods. A confirmed case was defined using criteria specified for the generalized form of meningococcal infection in accordance with the Sanitary and Epidemiological Regulations 126.96.36.1996-06 “On Prevention of Meningococcal Infection” introduced by Resolution No.34 (dated December 29, 2006) of the chief state sanitary doctor of the Russian Federation.
The disease criteria were clinical symptoms including a sudden rise in temperature to 38-39 C, intolerable headache, rigidity of neck muscles and mental confusion. Laboratory confirmation included turbid liquor, leukocytosis from 10 to 100 cells per mm3, prevailing neutrophils with a higher concentration of proteins and lower concentration of glucose, and isolation of Neisseria meningitidis. Serotyping was performed in the regional laboratory and the designated serotype was confirmed at the laboratory of the Federal State Research Institution “Central Research Institute of Epidemiology” of Rospotrebnadzor (Federal Service for Surveillance on Consumer Rights Protection and Human Well-Being).
Data was obtained from notifications received by a branch of the Federal State Health Institution (FSHI) “Centre of Hygiene and Epidemiology in the Republic of Komi in the City of Pechora”, from health institutions, patients’ medical charts, results of active clinical and bacteriological studies of contacts and from epidemiological studies related to all cases of the disease. The incidence of meningococcal infection among the city population for several years and data from the regional information bank regarding the etiological agent bank were analyzed.
Results and Discussion
The dynamics of meningococcal infection incidence rate among the city population over a thirty-year period does not show any definite cyclic tendencies. From 1980 to 2008 the incidence rate varied from 0 to 26 cases per 100,000 population. A significant decrease was observed after 1985 when the incidence rate did not rise over 11.5 per 100,000 population (Fig.1). Etiological investigations in the preceding period demonstrated the circulation of serotypes A and B.
Epidemiological monitoring showed that the outbreak occurred during seasonal increase in acute respiratory viral infections when these infections significantly exceeded the average incidence rates of previous years as well as estimated epidemic threshold levels. The majority of patients was children and teenagers. Paired serology showed the build-up of antibodies for influenza virus B and parainfluenza. This may have resulted in waning immunity among the population and may also have created favorable conditions for the epidemic spread of the circulating agent of meningococcal infection.
Six cases of meningococcal infection were registered on March 16-17 2009 in the city of Pechora. Five of the patients were children and teenagers aged 17 and younger, and one patient was 18 years old. All cases were severe and two cases had lethal outcomes. The reported clinical diagnoses included purulent meningitis (1 case); purulent meningitis, meningococcemia and meningoencephalitis (1 case); generalized form of meningococcal infection, meningococcemia and meningoencephalitis (1 case); generalized form of meningococcal infection, meningococcemia and meningitis (1 case); generalized meningococcal infection, fulminant form, meningococcemia with concomitant diagnoses of third degree infection toxic shock, disseminated intravascular coagulation (DIC) syndrome, acute adrenal insufficiency and Waterhouse-Friderichsen syndrome (2 cases). During the epidemiological investigation and active detection of contacts nine carriers of Neisseria meningitidis serotype С and 17 people with symptoms of nasopha ryngitis were found. All received adequate therapy. A total number of 833 people were examined and monitored by health care workers, among those 47 persons were from home contacts. Otolaryngologists were invited to take part in the examinations. A considerable number of contacts were traced because the diagnosed patients were mostly teenagers. Contacts were examined from the neighbourhood, various educational institutions and an entertainment site where teenagers congregated. As a result, preventive chemoprophylaxis was prescribed to 557 people. Most of the bacteria carriers and people with nasopharyngitis were found at the entertainment site that had unsatisfactory sanitary conditions (hot, humid, overcrowded and inadequate ventilation). An analysis of the cases helped to formulate an epidemiological diagnosis. A clustered focus of meningococcal infection among the children and teenagers in the city included the circulation of Neisseria meningitidis serotype С manifested as a disease or in the carrier state. The local population did not have any specific immunity for this infection. The infection was actively spread through contact between carriers and non-immune individuals. The predisposing factors for the development of this focus of infection included being a teenager, an increase in acute respiratory viral infections and contact between people in overcrowded places with poor ventilation.
In order to eradicate the foci of meningococcal infection and to stop the epidemic, the chief state sanitary doctor in the Republic of Komi issued a resolution recommending the immunization of all contacts . A vaccine with an antigen component of the detected pathogen was used. A total of 757 contacts of patients located at educational institutions, places of residence and entertainment sites were immunized. No new cases of the infection were registered.
Studies addressing the epidemiology of meningococcal infection indicate that after an inter-epidemic period the epidemic growth starts and, as a rule, happens quite unexpectedly . Effective serological monitoring of meningococcal infection and timely detection of the sources of infection are crucial for preventing epidemics . When conducting outbreak investigations and implementing control measures, it is necessary to investigate the circumstances under which a patient may come in close contact with carriers of the pathogen.
General practitioners should be aware of the danger of meningococcal infection during the seasonal epidemics of acute respiratory viral infections. Serotyping Neisseria meningitidis provides valuable information for epidemiological investigations of outbreaks and for the implementation of type-specifi c vaccines.
Immunization of risk groups based on characteristics of the epidemic and chemoprophylaxis of contacts will help to stabilize and improve the epidemiological situation.
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