The epidemiological situation of respiratory infections varies seasonally
Respiratory infections cause significant morbidity every year and place a burden on healthcare, especially from autumn to spring. The epidemiological situation varies seasonally, and the distribution of different viruses and bacteria changes depending on the time of year and epidemic conditions. Typically, several viruses and bacteria circulate simultaneously, which is reflected in fluctuations in detected case numbers and the need for hospital care.
Influenza
Influenza viruses cause annual epidemics, the timing, duration and intensity of which vary. Epidemics occur mainly in the winter season, typically from October to April. Different subtypes and lineages of influenza viruses may circulate at the same time, which can affect disease burden.
Quick report: Influenza weekly and by region
Coronavirus SARS-CoV-2
The SARS-CoV-2 coronavirus has become an established part of the overall respiratory infection landscape. Infections occur throughout the year, and case numbers fluctuate in waves. The most recent period of high case numbers was in autumn 2023.
In addition to reported communicable disease cases, the prevalence of coronavirus can be monitored by measuring viral genetic material in wastewater collected from sewer systems.
Weekly report on coronavirus wastewater surveillance (in Finnish)
Respiratory syncytial virus (RSV)
RSV epidemics typically occur in late autumn and winter, although the timing varies. The timing and extent of epidemics fluctuate each year. Long-term monitoring has shown that larger epidemics occur every other winter, and smaller ones in alternating years. Reported cases are concentrated especially among children aged 0–4 years and adults aged 75 years and older.
Quick report: RSV weekly and by region
Pneumococcus (Streptococcus pneumoniae)
In addition to mild upper respiratory infections, pneumococcal bacteria cause severe infections requiring hospital care, such as pneumonia, bacteraemia, sepsis and meningitis. Among children under 5 years of age, the number of severe pneumococcal infections has decreased since the introduction of the childhood vaccination programme in late 2010.
The vaccine introduced this year covers a larger proportion of pneumococcal types, and the number of infections among vaccinated children is expected to decrease further. Due to herd immunity, pneumococcal diseases caused by vaccine types are also expected to decrease in other age groups.
Quick report: Severe pneumococcal cases (pneumococcus detected in blood or cerebrospinal fluid) by week and region
Legionellosis
Legionella bacteria can proliferate in water systems or soil and cause Legionnaires’ disease, a severe form of pneumonia. The incidence of legionellosis and the proportion of domestic infections have increased in recent years.
The rise in case numbers is a global phenomenon, the exact causes of which are not known. In Finland, the increase may partly be explained by greater awareness and improvements in diagnostics. In 2025, the number of cases reached a record high, and infections caused by Legionella longbeachae originating from soil increased significantly. A similar rise in soil-associated cases has been observed elsewhere in the Nordic countries, but the underlying reasons remain unclear.
Quick report: Legionellosis by region
Reporting services
ILI and ARI visits and contacts in primary health care
Hospital care for acute respiratory infections in Finland (in Finnish)
Influenza activity by wellbeing services county and week based on ILI consultations, seasons 2022/2023–2025/2026 (in Finnish)
The Infectious Diseases Register statistical database – direct links to microbe-specific views:
Updated weekly report on coronavirus levels in wastewater:
Weekly report on coronavirus wastewater surveillance (in Finnish)
Background information
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Sources
Respiratory infection surveillance is based on national registers such as AvoHilmo, the Infectious Diseases Register and Hilmo.
Statistical description
The Finnish Institute for Health and Welfare (THL) maintains the national Infectious Diseases Register based on the Communicable Diseases Act and Decree. Laboratory-confirmed microbial findings are reported to the register. It provides access to detailed statistics on the number and incidence of infectious diseases.
The Care Register for Health Care (Hilmo) is a national data collection and reporting system for social welfare and health care.
The primary health care outpatient care notification system (Avohilmo) is part of the Hilmo system.
Hilmo and Avohilmo provide information on service use, access to care, population health problems and epidemics, health promotion services, and the division of labour and care practices among professionals.
Update schedule
Influenza statistics are published daily, SARS-CoV-2 and RSV information weekly, and pneumococcal and legionellosis statistics monthly.
