Data addressing the incidence of acute respiratory infections (ARI) in the Republic of Belarus in 2009 during the (Н1N1)2009 influenza epidemic and the results of virological investigation of clinical samples from ARI patients were analysed.
The influenza (Н1N1) epidemic in the Republic of Belarus developed in three stages during 2009 (Fig. 1).
The first stage (from April 26 to June 11, 2009) was characterized by a heightened threat of pandemic: the World Health Organization (WHO) raised the pandemic alert level from phase 4 to 5. A number of measures were taken in the Republic of Belarus to prevent import and spread of pandemic (H1N1)2009 influenza and to provide early laboratory diagnosis of the highly pathogenic influenza virus.
The second stage (from June 11 to October 1, 2009) started when phase 6 of the pandemic alert was declared and continued up to the beginning of the epidemic influenza season. Measures were mainly targeted at preventing the spread of pandemic influenza virus among the population including organized groups in the new school year.
The third stage (from October 1, 2009 to May 2010) was associated with the epidemic influenza season. During this period, a number of administrative, anti-epidemic and medical measures were taken in order to minimize the impact of the pandemic influenza virus.
The objective of the article is to analyze the epidemic situation for ARI in the Republic of Belarus during the period of spread of the pandemic influenza virus in 2009-2010.
Materials and Methods
Data from statistical reports on ARI incidence in the population during the 2009-2010 epidemic season were analyzed. Reports from 18 control cities, where 53% of the total population live, and the results of virological studies of clinical material from ARI patients that were analyzed by the enzyme-linked immunosorbent assay (ELISA), and PCR methods were used for the analyses.
ARI incidence in the Republic of Belarus was registered at a non-epidemic level during the first stage. During this period, the incidence in control cities varied from 371.4 to 616.3 cases per 100,000 population (Fig. 1). The average weekly incidence was 467.6 cases per 100,000 population. Among children, the incidence was 1499.5 cases per 100,000 population, which was 6.4 times higher than among adults (233.7 cases per 100,000 population). The highest incidence was registered among children under 5 years of age: 3092.0 cases. Among ARI patients who sought medical attention, children under the age of 18 prevailed (59.2%) and 55.5% were under the age of 5.
Fig. 1. ARI incidence in the Republic of Belarus from week 21, 2009, to week 2, 2010
The circulation of ARI pathogens was monitored daily and 847 samples were subjected to ELISA testing. In 155 samples (18.5%) the following viruses were found: 1.3% influenza A viruses, 7.7% parainfluenza viruses, 51% adenoviruses, 30.3% respiratory syncytial (RS) virus, and 9.7% of the samples yielded a combination of adeno- and RS viruses. Clinical samples from patients with severe respiratory symptoms were analyzed by PCR. The pandemic influenza virus A(H1N1)2009 was not detected among these samples.
During the second stage the incidence of ARI remained at a non-epidemic level (Fig. 1). The incidence in control cities varied from 274.4 to 950.0 per 100,000 population and the average weekly incidence was 433.9 per 100,000 population. Among children the incidence reached 1432.1 per 100,000 population, which was 7.1 times higher than among adults (201.3 per 100,000 population). The highest incidence was still registered among children under age of 5 years (55.5%): 2946.8 per 100,000 population. Among ARI patients who sought medical attention, children under the age of 18 prevailed (61%). During this period, 2283 clinical samples were subjected to laboratory analyses. The etiological structure of causal agents for respiratory diseases during the second stage was: 2.2% influenza А, 1.9% influenza В, 10.2% parainfluenza viruses, 32.7% adenoviruses, 32.4% RS viruses and 20.6% mixed infections. The A(H1N1)2009 influenza virus was found in 30% of all samples from imported cases.
The Ministry of Health of the Republic of Belarus extended the number of cohorts to be immunized using funds from the national and local budgets during the second stage. The cohorts included all groups at high risk for influenza complications: children from 6 months to 3 years of age; children from 3 years and adults with chronic diseases; people with immunosuppression; people over the age of 65; pregnant women. In addition, vaccination was provided to groups with a high risk of being infected with influenza including children from 3 to 6 years; schoolchildren from 6 to 16 years; healthcare workers; people from institutions with day-and-night stay of children or adults; ornithologists, workers in poultry enterprises; workers performing domestic maintenance services; teaching staff at educational institutions; trade and catering workers; transport workers; and specialists in contact with chronic immunocompromised patients and children under the age of 6 months.
As a result of the immunization campaign 1,044,202 people were vaccinated against the seasonal influenza in 2009. This is a coverage of 10.8% of the total population of the country as compared to 7% in 2008; 36.2% of the vaccinated were children and 63.8% adults.
Daily monitoring of pneumonia incidence was implemented during the third stage. Some ICU wards were reorganized to provide twenty-four-hour X-ray diagnostics, and day-and-night shifts were organized in ”on-duty” drugstores. From November 1, school vacations were extended and all mass public events were cancelled. Healthcare workers and representatives of the country life-support spheres were vaccinated against the pandemic (H1N1)2009 influenza. A total of 500,000 people were vaccinated.
ARI incidence in the Republic of Belarus rose during this period. The increase started earlier than usual (January-February) during week 44 (from October 26, 2009) and continued for 5 weeks (until November 29) as shown in Figure 1. From the beginning of the epidemic season in week 40, 2009 to week 2, 2010, a total of 1,088,710 cases of ARI and influenza were registered in control cities. The incidence was 20,779.5 per 100,000 population and the average weekly rate was 1398.8 per 100,000 population, which was 3 times higher than the non-epidemic incidence.
Fig. 2. Proportion of ARI patients in the Republic of Belarus by age groups from week 40, 2009 to week 2, 2010 (3rd stage)
During the third stage the adult population prevailed (Fig. 2). Adults accounted for 49.8% of ARI cases and increased to 57.4% during the period of epidemic growth. The incidence among adults was 4 times higher than during the non-epidemic period. The highest incidence was registered among children (3816.8 per 100,000 population), which was 4.4 times higher than the incidence among adults.
Compared with the first and second stages, the highest incidence among children was in the 5-14 years age group (3134.5 per 100,000 population). This group accounted for 44.2% of the infections.
From week 40 to week 48, 2719 samples were subjected to ELISA testing. The etiological structure of ARI was: 18.8% influenza А, 2.7% influenza В, 11.6% parainfluenza viruses, 20.2% adenoviruses, 26.5% RS viruses, and 20.2% mixed infections. A total of 1714 samples from patients with severe clinical forms of ARI and pneumonias were analyzed by PCR. The A(H1N1)2009 influenza virus was found in 20% of cases; 82.8% of the pandemic influenza cases were adults of which 37% were among 18-29 year olds.
During the period of epidemic growth and at the peak of the epidemic process, pandemic influenza viruses prevailed in the clinical samples. Pandemic influenza viruses were detected in clinical samples from patients with confirmed laboratory diagnoses. The diagnosis was later confirmed by the WHO Diagnostics Centre in London and the State Research Centre of Virology and Biotechnology VECTOR of Rospotrebnadzor (Federal Service for Surveillance on Consumer Rights Protection and Human Well-being) in Novosibirsk (Russian Federation).
After the incidence of respiratory infections fell to a non-epidemic level, the circulation of pandemic influenza virus was monitored in control cities at the sentinel surveillance level. The monitoring results showed that the circulation of the pandemic virus was also lower. In December 2009 the pandemic influenza virus was detected in 32.5% of the investigated samples. In January 2010 the proportion of positive samples was only 1.8% indicating sporadic incidence of the pandemic virus А(Н1N1)2009. Among patients with the laboratory-confirmed (H1N1)2009 influenza, 49.9% of cases were severe, 45.1% were moderate and 5% of the cases were mild. The severity of clinical manifestations ranged from subclinical and asymptomatic to severe forms with lethal outcomes. Respiratory complications were observed in 49.9% of the cases, 10% experienced cardiovascular complications, and 4% had urinary complications. Risk factors were associated with 48% of the patients (36.5% chronic pathology, 12.3% obesity, 11.2% pregnancy). Only 2.7% of the patients had been previously vaccinated against the seasonal influenza.
The clinical presentation of the diseases caused by the pandemic virus А(Н1N1)2009 coincided with the clinical symptoms of the illness registered in other countries. The anti-epidemic, medical, drug supply and information measures helped to control the ARI epidemic situation and to minimize the consequences of the global (H1N1)2009 influenza pandemic in the Republic of Belarus.