Epidemiology and impact of influenza in Mongolia, 2007-2012

Background

Mongolia's Health Service began to conduct surveillance for influenza in the 1970s. This surveillance has become more comprehensive over time and now includes 155 sentinel sites in Mongolia. In this study, we analyzed the epidemiological characteristics and impact of influenza using data from influenza surveillance in Mongolia.

Materials and methods

The data were collected by the National Influenza Center, Mongolia (NIC). Incidence rates of influenza-like illness (ILI) and severe acute respiratory infections (sARI) were calculated as the proportion of the number of ILI and sARI cases to the total population in the studied areas. Nasopharyngeal samples were collected and tested using real-time reverse transcription polymerase chain reaction [(rt)-RT-PCR]. Selected samples negative for influenza were tested for other respiratory pathogens by multiplex rt-RT-PCR.

Results

Averages of 14·0 ILI and 0·8 sARI episodes per 100 population per year were observed during the five influenza seasons. The highest incidences of influenza associated with ILI and sARI were observed among children 0–4 years old. The number of ILI cases showed a clear seasonality, generally peaking between December and February. In contrast, sARI incidence peaked twice during each season. Influenza B was most prevalent during 2007–2008 and 2011–2012, influenza A (H3N2) during 2010–2011, seasonal A (H1N1) during 2008–2009, and A (H1N1) pdm09 during 2009–2010.

Conclusions

Additional data on the epidemiology and impact of influenza including socioeconomic impact and vaccine effectiveness are required to develop a national influenza control policy, including a vaccination strategy. Our results provide useful data for developing such a policy.

[Genotyping of varicella zoster virus strains isolated in Mongolia]

This study analyzed 50 varicella zoster virus (VZV) samples collected during 2004 to 2007 from patients with VZV infection, who were treated at the National Center of Communicable Diseases, Ulan-Bator, Mongolia. The method based on amplification of specific DNA fragments of the ORF21, ORF22, and ORF50 genes was used, followed by the sequencing and detection of the status of characteristic point mutations in these fragments. The results indicated that the collected samples belonged to genotypes J (62%), M1 (18%), E1 (12%), E2 (4%), and M2 (4%). Moreover, restriction endonuclease polymorphism in ORF 62 for the cleavage site Smal and Mspl, in ORF 38 and ORF 54 for the cleavage site Pstl and Bgll were analyzed. All the samples were Sma- Msp-. All samples with genotype E were Pst+ Bgl-; all samples with genotype M1 and M2 were Pst+ Bgl+. Out of 31 samples with genotype J, 29 and 2 were Pst+ Bgl+ and Pst+ Bgl+, respectively. The study could identify the genotypes of VZV circulating in Mongolia and confirmed the absence of mutations characteristic for the vaccine strain.