Infectious Disease Epidemiology Annual Report - 2021

full report in German

The Infectious Disease Epidemiology Annual Report provides an overview and assessment of infectious diseases data as reported to the Robert Koch Institute (RKI).

The coronavirus disease (COVID-19) continued to be the primary notifiable infectious disease in the year 2021. Not only did the COVID-19 pandemic place an enormous burden on the public health system in Germany, it also affected the occurrence and detection of other notifiable infectious diseases. In order to better understand the impact of the COVID-19 pandemic on other notifiable infectious diseases, chapter 4.4 presents further analyses regarding the difference between the expected number of cases and the actual number of cases in 2021. A comparison between the two pandemic years will also be provided.

The number of reported cases of almost all notifiable infectious diseases in 2021 was substantially lower as compared to the period before the COVID-19 pandemic.

Especially noteworthy was the exceptionally low number of influenza cases. Neither in Germany nor in other European countries was there evidence of a measurable influenza wave at the population level for the 2020/21 season. This can be attributed to, among others, the national and international measures taken to contain the COVID-19 pandemic, which mayalso have affected the transmission of other respiratory transmissible pathogens.

Additionally, fewer cases were observed for human to human transmitted diseases such as measles, whooping cough, mumps and chickenpox. There were varying developments concerning gastrointestinal infections. While the cases for rotavirus gastroenteritis remained approximately the same as in 2020, there were more cases for norovirus gastroenteritis, shigellosis and EHEC disease. In the case of nosocomial infections, such as invasive infection with MRSA or severe Clostridioides difficile disease, more cases were again observed compared to the previous year. Among sexually and blood-borne infections, a decrease in the number of cases of syphilis and hepatitis B was observed, while the number of cases of other infections, such as HIV infections, remained more or less the same.

Typical travel-associated diseases, such as dengue fever, were reported less frequently. Only malaria showed an increase compared to 2020, although the number of cases remained well below pre-pandemic levels.

The reasons for these changing dynamics are multifactorial, as well as disease- or pathogen-specific. In addition to possible changes in the use of or access to health care services, public health measures taken in the wake of the COVID-19 pandemic, e.g., contact restrictions, distance and hygiene rules, but also school and daycare closures and travel restrictions, may have led to a real change in the transmission dynamics of other infectious diseases. However, conclusive statements on causality cannot be made based on an analysis of the available reporting data alone.

More cases of hantavirus disease were observed in 2021 than in 2020. Due to the correlation between the density of the rodent population and the beech mast in previous years, strong annual fluctuations are typical for hantavirus disease. Following a strong beech mast in 2020, the incidence of hantavirus disease in southern and western Germany, mainly caused by Puumalavirus, was again very high, but did not reach the level of the previous record year in 2012.

Despite the sharp decline in case numbers, the gastrointestinal diseases campylobacter enteritis, norovirus gastroenteritis, and rotavirus gastroenteritis remain among the most common notifiable infectious diseases, as in previous years.

In 2021, the COVID-19 pandemic and the emergence of viral variants of concern again highlighted the importance of an integrated molecular surveillance, in which the results from pathogen typing are evaluated together with data from the reporting system based on the IfSG.

Molecular surveillance also plays a very important role in the detection of outbreaks. In particular, cases that occur over a longer period of time can be more easily assigned to a protracted outbreak. In this manner, 70 transmitted cases of Salmonella Braenderup could be attributed to a large multinational outbreak with a total of more than 300 cases. Galiamelons from Honduras were identified as the infection vehicle by means of epidemiological studies and detection of the outbreak strain in the food and at the production site.