Influenza season 2023-2024/ Seasonal influenza and Covid-19: Health alert

The high proportion of outpatient visits for influenza-like illness is linked to the concomitant circulation of respiratory syncytial virus and SARS-CoV-2, according to the Directorate for Epidemiology and Disease Control.

The Ministry of Health and Social Protection has just published the epidemiological bulletin on influenza and severe respiratory infections for the 2023-2024 season. In its bulletin, the Department of Epidemiology and Disease Control reports that, for the 2023-2024 season, the “epidemic threshold” estimated at 1.94% was reached in S45/2022, seven weeks ahead of previous seasons, excluding the pandemic season, and the “average epidemic threshold” estimated at 2.1% was crossed in S46/2023. Since week S36/2022, the indicator monitoring influenza activity has been rising sharply, albeit with considerable fluctuation, over an eight-week period. This level of activity is similar to past seasons (2021-2022 and 2022-2023) at the same period.

Among outpatient consultations for influenza-like illness, the 25-59 and 15-24 age groups accounted for the highest proportions, 32.4 and 20% respectively, as usually observed in previous seasons, excluding the pandemic season. The increase in influenza activity observed well above the seasonal average is thought to be associated in particular with the high symptomatological similarity between influenza-like illness and Covid-19, and with the co-circulation of other respiratory viruses, notably respiratory syncytial virus (RSV).

For virological surveillance of influenza and acute respiratory infections (ARI), the monitoring indicator is the virological test positivity rate, corresponding to the weekly number of positive results in relation to tests carried out by laboratories. During this season, virological surveillance was revitalized and activated as of week S40 of 2023, thanks to the contribution of sentinel hospital laboratories and the availability of the GeneXpert molecular diagnostic test, enabling the simultaneous detection of three pathogens: influenza viruses, Sars-CoV -2 and RSV.

From week S40/2023 to week S47/2023, a total of 422 nasopharyngeal samples were collected, including 217 cases of IRAS (51.4%) and 205 cases of ILI (48.6%). No cases of seasonal influenza were diagnosed among all samples collected and tested during this period. On the other hand, RSV tests were positive in 15.4% of cases, mainly in pediatric patients, and SARS-CoV-2 tests were positive in 4.74% of cases.

These data show that, during the current flu season, there was slight circulation of SARS-CoV-2 and RSV, while no active circulation of influenza viruses was diagnosed. The high proportion of outpatient visits for influenza-like illness (ILI) is more likely due to the concomitant circulation of respiratory syncytial virus (RSV), a very common virus that causes respiratory tract infections, especially in young children, and SARS-CoV-2. Respiratory syncytial virus (RSV) is the most frequent cause of acute lower respiratory tract infection and hospitalization in children.

In Morocco, influenza surveillance is carried out by a sentinel system whose objectives are to monitor the evolution of seasonal influenza, estimate the burden of disease, identify circulating viruses and monitor their sensitivity to antivirals. It is based on two main components, namely clinical surveillance of influenza-like illness (ILI) through an ambulatory network of 412 health centers, operating in all provinces and prefectures serving a population of almost 12 million. The second component is based on epidemiological and virological surveillance of influenza syndrome and severe acute respiratory infections, carried out at 10 sentinel sites (Tangier, Rabat, Fez, Meknes, Marrakech, Béni Mellal, Oujda, Agadir Casablanca and Laâyoune), as well as through a network of volunteer doctors in private practice.

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