Medicine/9

Medicine/9.Hygiene and epidemiology

Candidate of biological sciences, assistant professor of epidemiology Korneev A.G.

Student preventive health department Krivulya Y.S.

Orenburg State Medical Academy, Russia

ON ASSESSMENT OF THE BACKGROUND INCIDENCE OF THE ORENBURG REGION POPULATION WITH HEMORRHAGIC FEVER WITH RENAL SYNDROME (RUSSIA)

The estimation of the background incidence rate is an essential part of the epidemiological surveillance. The background incidence of hemorrhagic fever with renal syndrome (HFRS) is supposed to include countryside morbidity mainly in case when located within the natural focus. City residents are more dynamical and can get infected at different remoted natural focuses. The current research purpose is to verify this hypothesis.

The study was held at the hospitals of the Orenburg region: Orenburg (the regional centre; the population is 526.000 people), Buguruslan (52.000 people), Buzuluk (89.000 people) and Kuvandyk (28.000 people). During the study there were examined case histories of HFRS in-patients who had been registered within the period of time from 2005 to 2012. The case histories were chosen by means of randomization (248 pieces from Orenburg and 150 pieces from the three other towns); few of them were rejected as defective for the scant epidemiological anamnesis. All of the settlements are situated at the natural focuses of HFRS. The trapped rodents (voles and harvest mice) as well as the infected patients proved to have Puumala virus of HFRS (Genus: Hantavirus) [1]. The data of the Federal public health agency "Centre of Hygiene and Epidemiology" were also used.

According to the case histories, the patients of every settlement were divided into 2 groups: the urban and rural residents. Thus, in the hospitals of Orenburg there were 49 cases of HFRS in the rural patients and 193 cases in the urban ones. Having analyzed the epidemiological anamneses we revealed that the patients from villages of the Orenburg district had got infected within its territory in 75,5% of cases. 46,9% of these patients considered their houses to have been the placeof the infection, 14,2% assumed that they had got contaminated through agricultural work, and 38,8% - through fishing, hunting and mushroom picking. It is noteworthy that the urban residents correlate the fact of the infection with the territory of the Orenburg district only in 14,5% of the cases, 2,6% consider their houses to have been the place of the infection, 2,1% mentioned the gardens and 5,2% - the workplaces. In 81,9% of the epidemiological anamneses there were mentioned other districts, which the patients had visited for different purposes.

In 52% of the cases it was fishing that had motivated the urban residents for a drive to the natural focuses of HFRS beyond the territory of the Orenburg district, in 10% of the cases it was hunting. 18% of the patients visited the woods or floodplains in order to pick mushrooms and berries and to have a picnic. There are five officially registered natural focuses of HFRS within the territory of the Orenburg region. It should be noted that the natural focus in Ural bottom lands is the most visited one; 120 km distant from Orenburg, it is remarkable for the abundant flood-land vegetation which is easily detectable among the landscape of the Orenburg region prairies. The floodplain width is approximately 20 km; its moisture, opulent vegetation, stable forage base provide with favourable conditions not only big animals but also small rodents, which carry the HFRS virus. Among the Orenburg region prairies the Ural bottom lands are the most inhabited with voles – the main reservoir of Puumala virus of HFRS (Genus: Hantavirus).

The situation described above is different from that registered in smaller towns of the Orenburg region (Buguruslan, Buzuluk and Kuvandyk). 100% of the rural in-patients with HFRS considered their rural region to be the place where they had got the infection; 80-100% of them denoted their own houses. The towns residents considered that they had got the infection within the house in 25-50% of the cases; however, more than 50% supposed to have got infected at the territory of the district. It should be noted that small towns way of life is very often close to that in thevillage. Over 95% of the diseased with HFRS urban patients live in private houses, have an attached garden and domesticated animals. These conditions are perfect for small rodents which are Hantaviruses carriers. Orenburg in its turn is a regional centre and provides absolutely different conditions by means of numerous apartment buildings. It is unlikely to get infected from rodentswithin the city area. There are some sporadic cases registered in garages, cellars, etc., which are situated in the suburbs. This keeps happening mainly during the years of epidemic rise of morbidity.

Table 1.

Long-term average HFRSincidence in the urban and rural patients within the territories of the Orenburg region (2005-2012)

The localities	The urban patients (towns)	the rural patients (villages)
Buguruslan	38,35±8,55	49,88±15,00
Buzuluk	37,68±6,51	68,73±14,32
Kuvandyk	55,08±13,95	35,62±12,52
Orenburg	17,27±1,81	22,88±5,56

We haven't revealed statistically significant distinctions between the incidences among the urban and the rural patients within the neighbouring territories (Table 1). Nevertheless, despite the fact that there is no difference between the incidence rates, it is stated that the in-patients of the regional centre get infected with HFRS when leaving their district (85.5% of the cases). It is correctly to consider the morbidity rate among the rural population as the background incidence rate.

Literature

1. Garanina, S.B., Genetic diversity and geographic distribution of hantaviruses in Russia / S.B. Garanina [et al.] // Zoonoses Public Health. - 2009 Aug;56(6-7):297-309.