Cases of influenza continue to be reported from all areas of the country. By the third week of May 2015, the Medical Research Institute has tested 252 samples positive for influenza; influenza A - 170 and influenza B – 82.
Current situation of seasonal influenza in Sri Lanka
The influenza viruses
Seasonal influenza viruses are largely grouped as A, B and C. The Influenza A virus sub types H1N1 and H3N2 have been in circulation in the country causing influenza recently. In addition, there are two type B viruses that are also circulating as seasonal influenza viruses. Influenza C poses much less of a disease burden. Globally, seasonal influenza has shown a decreasing trend according to the World Health Organization surveillance data. Similarly in tropical Asia, influenza activity has been low during the recent past (WHO 2015).
Global burden of influenza
Based on FluNet (the World Health Organization global tool for influenza virological surveillance), during the latter half of April and early May 2015, 26.1% of the globally tested samples have been influenza A while 73.9 % were reported to be influenza B. Of the sub typed influenza A viruses, 53.8% were influenza A (H1N1) pdm09 and 46.2% were influenza A (H3N2).
Burden of influenza in Sri Lanka
During the first week of March 2015, seven suspected cases of influenza were reported to the Epidemiology Unit from Thissamaharama, which included five pregnant women and two children. Of the pregnant women two were positive for influenza A. However, on further investigation the cases were found to be geographically scattered.
Cases of influenza continue to be reported from all areas of the country. This year up to the third week of May, the Medical Research Institute has tested 252 samples positive for influenza; influenza A - 170 and influenza B – 82. Out of the 78 influenza A cases that were sub typed there had been 42 Influenza A H1N1 cases (National Influenza Center 2015). It was also noted that four pregnant women who died during the months of April and May have been found to be positive for influenza A.
Sentinel site surveillance of influenza
Epidemiology Unit, Sri Lanka conducts influenza sentinel sites surveillance at 19 selected hospitals in order to check the current circulating viral pattern. Surveillance is carried out for Influenza Like Illness (ILI) and Severe Acute Respiratory Infection (SARI). ILI is defined as an acute respiratory illness with measured temperature 38 0 C or more and cough, with onset within the past ten days. SARI is defined as requiring hospitalization in addition to the features of ILI (WHO 2014). Samples of nasopharyngeal aspirates are collected up to 10 per month from ILI patients and up to 05 per month from SARI patients.
Of the 111 ILI samples collected during March 2015, 07 samples were positive for influenza A (influenza A H1N1 – 05, influenza A H3N2 01, un-typed – 01) and 11 samples were positive for influenza B. Among the 19 SARI samples received during March 2015, 01 has been positive for influenza A H3N3.
It was noted that from March 2015 to April 2015, the number of total SARI patients reported has increased by about 1%.