The epidemiology of influenza varies depending on locale. Influenza is generally associated with seasonal (winter)
epidemics in temperate region, but all year – round pattern with a rainy season peak is observed in the tropical regions.
The Nigeria Influenza Sentinel Site Surveillance is a modified form of global Influenza surveillance and is an all year
programme. This involves search for Influenza – like illness (ILI) and severe acute respiratory illness (SARI) in some
selected sentinel site hospitals. This study is part of the National Influenza sentinel site surveillance as Nnamdi Azikiwe
University Teaching hospital (NAUTH) Nnewi in Anambra state Southeast Nigeria is one of the sentinel site facilities. The
few epidemiologic studies of human influenza in the country indicate that sporadic cases of influenza may occur
throughout the year and that sporadic outbreaks do occur mainly during the rainy season or during times of the year with
lower environmental temperatures. The influenza sentinel site surveillance at Nnewi – a unique geographical position in
Southeast Nigeria will provide an efficient and reliable means of obtaining epidemiological and laboratory data regarding
the disease burden, seasonality, and strain circulation. These data will critically inform prevention and control strategies.
This is a cross – sectional, prospective and hospital based study. NAUTH Nnewi represents the Southeast zone of the 4
sites activated for Influenza Surveillance in Nigeria. Anambra state has an area of 4.844SqKm and a population of
4,055,048 by 2006 census. It has a population density of 840/Km2
. It is located in the warm tropical climate with relatively
high temperature throughout the year. It has two seasons-rainy or wet season that last from mid-March to November and
the Dry season that occupies the rest of the year. It has a mean annual temperature of 27oC. The amount of rainfall is April
– September =141.2cm, percentage of rainfall is 78% and October – March = 39.9cm with percentage of rainfall as 22%. The
methodology used is according to the Federal Ministry of Health (FMOH) Nigeria protocol for national Influenza sentinel
surveillance (FMOH. Protocol for National Influenza Sentinel site Surveillance: Epidemiology Department, Nigeria Centre
for Disease Control, Revised Dec. 2011. P 6-12). A convenient sampling method was adopted in this study. Total number of
samples collected from January – December 2011that met the ILI and SARI criteria were 347 out of the expected 832 by the
sampling method used. Cases of ILI and SARI were seen throughout the year with the highest incidence for both occurring
in July. The collected samples were sent to Influenza Reference Laboratory, out of which 305 were processed. Total ILI
cases were 226(65.10%) while SARI cases were 121(34.90%). Out of the 305 processed, 278 tested negative, while there
were 13 cases of Influenza type A and 10 of Influenza type B. Of the type A 7 were females while 6 were males. Also for
type B 6 were females while 4 were males. Meanwhile 153 females and 125 males tested negative. Four cases were
missing. The most affected age group for both ILI and SARI was 0-4 years with 111 ILI cases and 78 SARI cases while the
age group 10-14 years is the least affected with 4 ILI and 3 SARI cases. The male (M): female (F) ratio for ILI is 103:123
while for SARI cases the ratio of M:F is 59:62. The study showed that acute respiratory infection occurs throughout the
year with the highest incidence occurring in July which is the coldest and most rainy period of the year. The existence of
Influenza type A and type B among the population was established and occur sparingly throughout the year. The target
population for control and treatment is the under five. The percentage hospitalization due to SARI cases peaked in July
which is the period with the highest burden of severe acute respiratory infection in the region. The implementation of
Influenza Sentinel Surveillance enabled characterization of the epidemiology and seasonality of influenza in South East
Nigeria for the first time. Future efforts should determine the population-based influenza burden to inform interventions
such as targeted vaccination