Estimated Number of Symptomatic Lyme Borreliosis Cases in Adults in Finland in 2021 Using Seroprevalence Data to Adjust the Number of Surveillance-Reported Cases: A General Framework for Accounting for Underascertainment by Public Health Surveillance

Background: Finland conducts public health surveillance for Lyme borreliosis (LB) based on clinically diagnosed and laboratory-confirmed cases. We used data from seroprevalence studies to determine the extent to which LB cases were underascertained by public health surveillance. Methods: The numbers of incident symptomatic LB cases in 2011 in six regions in Finland were estimated using (1) data from Borrelia burgdorferi sensu lato seroprevalence studies, (2) estimates of the proportion of LB infections that are asymptomatic, and (3) estimates of the duration of LB antibody detection. The numbers of estimated incident symptomatic LB cases were compared with the numbers of surveillance-reported LB cases to estimate regional underascertainment multipliers. Underascertainment multipliers were applied to the numbers of surveillance-reported LB cases in each region in 2021 and summed to estimate the number of symptomatic LB cases in Finland among adults in 2021. A sensitivity analysis evaluated the impact of different durations of antibody detection. Results: Using an asymptomatic proportion of 50% and a 10-year duration of antibody detection, the estimated regional underascertainment multipliers in Finland ranged from 1.0 to 12.2. Applying the regional underascertainment multipliers to surveillance-reported LB cases in each region and summing nationally, there were 19,653 symptomatic LB cases in Finland among adults in 2021 (526/100,000 per year). With 7,346 surveillance-reported LB cases in Finland among adults in 2021, the estimated number of symptomatic LB cases indicate that there were 2.7 symptomatic LB cases for every surveillance-reported LB case among adults. With a 5- or 20-year duration of antibody detection, there were an estimated 36,824 or 11,609 symptomatic LB cases among adults in 2021, respectively. Discussion: Finland has robust public health surveillance for LB, but cases are underascertained. This framework for estimating LB underascertainment can be used in other countries that conduct LB surveillance and have conducted representative LB seroprevalence studies.

[1]  B. Gessner,et al.  Incidence of Lyme Borreliosis in Europe from National Surveillance Systems (2005–2020) , 2023, Vector borne and zoonotic diseases.

[2]  B. Gessner,et al.  Seroprevalence of Lyme Borreliosis in Europe: Results from a Systematic Literature Review (2005–2020) , 2023, Vector borne and zoonotic diseases.

[3]  D. Swerdlow,et al.  Estimates of Presumed Population Immunity to SARS-CoV-2 by State in the United States, August 2021 , 2021, medRxiv.

[4]  G. Stanek,et al.  Infections with Tickborne Pathogens after Tick Bite, Austria, 2015–2018 , 2021, Emerging infectious diseases.

[5]  D. Swerdlow,et al.  Estimation of US SARS-CoV-2 Infections, Symptomatic Infections, Hospitalizations, and Deaths Using Seroprevalence Surveys , 2021, JAMA network open.

[6]  H. Wilking,et al.  Dynamics of Borrelia burgdorferi-Specific Antibodies: Seroconversion and Seroreversion between Two Population-Based, Cross-Sectional Surveys among Adults in Germany , 2020, Microorganisms.

[7]  M. Virtanen,et al.  Lyme borreliosis in Finland: a register-based linkage study , 2019, BMC Infectious Diseases.

[8]  J. A. Cárdenas-de la Garza,et al.  Clinical spectrum of Lyme disease , 2018, European Journal of Clinical Microbiology & Infectious Diseases.

[9]  J. Hänninen,et al.  Tick-borne pathogens in Finland: comparison of Ixodes ricinus and I. persulcatus in sympatric and parapatric areas , 2018, Parasites & Vectors.

[10]  J. Ollgren,et al.  Population-based Borrelia burgdorferi sensu lato seroprevalence and associated risk factors in Finland. , 2017, Ticks and tick-borne diseases.

[11]  M. Kuusi,et al.  Lyme Borreliosis in Finland, 1995–2014 , 2017, Emerging infectious diseases.

[12]  J. Hänninen,et al.  Crowdsourcing-based nationwide tick collection reveals the distribution of Ixodes ricinus and I. persulcatus and associated pathogens in Finland , 2017, Emerging microbes & infections.

[13]  P. Forsberg,et al.  A prospective study on the incidence of Borrelia burgdorferi sensu lato infection after a tick bite in Sweden and on the Åland Islands, Finland (2008-2009). , 2016, Ticks and tick-borne diseases.

[14]  J. Hänninen,et al.  Assessing the abundance, seasonal questing activity, and Borrelia and tick-borne encephalitis virus (TBEV) prevalence of Ixodes ricinus ticks in a Lyme borreliosis endemic area in Southwest Finland. , 2016, Ticks and tick-borne diseases.

[15]  C. Tufanaru,et al.  Methodological guidance for systematic reviews of observational epidemiological studies reporting prevalence and cumulative incidence data , 2015, International journal of evidence-based healthcare.

[16]  M. Kretzschmar,et al.  Measuring underreporting and under-ascertainment in infectious disease datasets: a comparison of methods , 2014, BMC Public Health.

[17]  J. Ernerudh,et al.  Prevalence, Diversity, and Load of Borrelia species in Ticks That Have Fed on Humans in Regions of Sweden and Åland Islands, Finland with Different Lyme Borreliosis Incidences , 2013, PloS one.

[18]  W. van Pelt,et al.  A Prospective Study among Patients Presenting at the General Practitioner with a Tick Bite or Erythema Migrans in the Netherlands , 2013, PloS one.

[19]  M. Widdowson,et al.  Foodborne Illness Acquired in the United States—Major Pathogens , 2011, Emerging infectious diseases.

[20]  R. Tauxe,et al.  Foodborne Illness Acquired in the United States—Unspecified Agents , 2011, Emerging infectious diseases.

[21]  Marc Lipsitch,et al.  Estimates of the Prevalence of Pandemic (H1N1) 2009, United States, April–July 2009 , 2009, Emerging infectious diseases.

[22]  Helmut Kerl,et al.  Clinical relevance of different IgG and IgM serum antibody responses to Borrelia burgdorferi after antibiotic therapy for erythema migrans: long-term follow-up study of 113 patients. , 2006, Archives of dermatology.

[23]  A. Steere,et al.  Persistence of the antibody response to the VlsE sixth invariant region (IR6) peptide of Borrelia burgdorferi after successful antibiotic treatment of Lyme disease. , 2003, The Journal of infectious diseases.

[24]  R Ruthazer,et al.  Persistence of immunoglobulin M or immunoglobulin G antibody responses to Borrelia burgdorferi 10-20 years after active Lyme disease. , 2001, Clinical infectious diseases : an official publication of the Infectious Diseases Society of America.

[25]  H. Soini,et al.  Prevalence of Borrelia burgdorferi inIxodes ricinus Ticks in Urban Recreational Areas of Helsinki , 1999, Journal of Clinical Microbiology.

[26]  L. McCaig,et al.  Food-related illness and death in the United States. , 1999, Emerging infectious diseases.

[27]  B. Svenungsson,et al.  Serological follow-up after treatment of patients with erythema migrans and neuroborreliosis , 1994, Journal of clinical microbiology.

[28]  G. S. Moore,et al.  FOODBORNE ILLNESS , 1990, The Lancet.

[29]  R. Rubini-Costa,et al.  产前诊断和干预改善结节性硬化症儿童的发育和癫痫结局 , 2022, Developmental Medicine & Child Neurology.

[30]  D. Grujičić,et al.  Infections I , 2011, Intensive Care Medicine.

[31]  P. Wahlberg,et al.  IgG seroprevalence of Lyme borreliosis in the population of the Aland Islands in Finland. , 1998, Scandinavian journal of infectious diseases.