Varicella and Herpes Zoster in Bulgaria (2023–2025): Harmonized Administrative Health Data on Healthcare Utilization, Vaccination, and Sick Leave in the Post-COVID Pre-Vaccine Period

Description This dataset provides harmonised administrative and surveillance health data describing the epidemiology and health system burden of varicella (ICD-10: B01) and herpes zoster (ICD-10: B02) in Bulgaria during the period 2023–2025. The analysed time window corresponds to the post-COVID-19 period and precedes the introduction of mandatory varicella vaccination (2026), providing an important baseline for evaluating vaccination policies and monitoring changes in disease epidemiology. The dataset integrates aggregated information from several national administrative and surveillance systems: 1. National Health Insurance Fund (NHIF) – hospital reimbursement through clinical pathways. 2. National Health Information System (NHIS) – national digital health infrastructure containing information on hospitalisations, outpatient medical examinations, and vaccination administration. 3. National Social Security Institute (NSSI) – sick leave records, sick leave duration, and compensation payments. 4. National Statistical Institute (NSI) – population denominators used for epidemiological rate calculations. National infectious disease surveillance system – mandatory reporting of infectious diseases according to Bulgarian public health legislation. All datasets are aggregated administrative records and contain no personally identifiable information. Data are aggregated at the regional (oblast) level and reported at monthly resolution, except for population denominators, which are annual. Regional names have been standardised to English transliterations, while the original Bulgarian names are preserved. All financial variables in this dataset are reported in Bulgarian lev (BGN), which was the official currency of Bulgaria during the study period 2023–2025. Bulgaria adopted the euro (EUR) in 2026. However, the Bulgarian lev had long operated under a currency board arrangement with a fixed exchange rate to the euro. The official fixed exchange rate was: 1 EUR = 1.95583 BGN This exchange rate remained unchanged throughout the study period and can be used to convert financial variables in this dataset to euros for international comparison. Case Definition and Surveillance Classification Case definitions follow Ordinance No. 21 of 18 July 2005 on the registration, notification and reporting of infectious diseases, issued by the Bulgarian Ministry of Health. Clinical criteria A person presenting with: acute onset fever moderately impaired general condition polymorphic pruritic rash consisting of macules, papules, vesicles and crusts Laboratory criteria Laboratory confirmation may include: detection of varicella-zoster virus antigen detection of virus-specific antibodies viral isolation detection of viral nucleic acid Epidemiological criteria person-to-person transmission exposure to a common source of infection Case classification Classification Definition Possible case Meets clinical criteria Probable case Meets clinical criteria and has an epidemiological link Confirmed case Meets clinical and laboratory criteria During outbreaks, a case meeting clinical criteria and having an epidemiological link may also be classified as confirmed. Diagnoses included in the dataset The dataset contains healthcare utilisation and surveillance data related to the following ICD-10 diagnoses: Varicella (B01) ICD-10 code Description B01.0 Varicella meningitis B01.2 Varicella pneumonia B01.8 Varicella with other complications B01.9 Varicella without complications Herpes zoster (B02) ICD-10 code Description B02.0 Zoster encephalitis B02.1 Zoster meningitis B02.2 Zoster with nervous system complications B02.7 Disseminated herpes zoster B02.8 Zoster with other complications B02.9 Herpes zoster without complications Clinical Pathways (NHIF) Hospital care in Bulgaria is reimbursed through clinical pathways defined by the National Health Insurance Fund. The dataset includes the following pathways: 1. KP104 - Diagnosis and treatment of contagious viral and bacterial diseases with complications. Minimum hospital stay: 3 days KP57.1 / KP57.2 - Diagnosis and treatment of acute and chronic viral, bacterial, spirochetal, mycotic and parasitic meningitis, meningoencephalitis and myelitis. Minimum hospital stay: 5 days (57.1 for children under 18, 57.2 for adults) KP93 - Diagnosis and treatment of severe bacterial infections of the skin. Files and Variables The dataset contains the following files. varicella_bgr_nhif_clinical_pathways.csv Hospital reimbursement records from the National Health Insurance Fund. Each row represents aggregated data for: month clinical pathway ICD-10 diagnosis Variables Variable Type Description date Date Reporting month clinical_pathway Character NHIF clinical pathway code icd10_code Character ICD-10 diagnosis code n_patients Integer Number of treated patients payment_bgn Numeric Total reimbursement paid by NHIF varicella_bgr_nhis_hospitalisations.csv Hospitalisations recorded in the National Health Information System. Variables Variable Type Description year Integer Calendar year month Integer Month region Character Harmonised region name region_bg Character Original Bulgarian region name age_cat Character Age group Diagnosis variables Counts of hospitalisations for each diagnosis: icd_b01_0 icd_b01_2 icd_b01_8 icd_b01_9 icd_b02_0 icd_b02_1 icd_b02_2 icd_b02_7 icd_b02_8 icd_b02_9 Values represent number of hospital admissions. varicella_bgr_nhis_medical_exams.csv Outpatient consultations recorded in the National Health Information System. Variables are identical to the hospitalisation dataset, but values represent the number of outpatient medical examinations. varicella_bgr_nhis_vaccinations.csv Vaccination records for the varicella vaccine (Varivax). During the study period, varicella vaccination was not part of the mandatory national immunisation programme and was typically paid for privately. Variables Variable Type Description year Integer Calendar year month Integer Month region Character Harmonised region name region_bg Character Original Bulgarian region age_cat Character Age group n_immunisations Integer Number of administered vaccine doses dose Integer Vaccine dose number (1 or 2) varicella_bgr_nssi_sick_leave.csv Sick leave records from the National Social Security Institute. Variables Variable Type Description region Character Harmonised region region_bg Character Original Bulgarian region month Date Reporting month type Character Sick leave type icd_code Character ICD-10 diagnosis sick_leave_num Integer Number of sick leave episodes sick_leave_days Integer Total number of sick leave days payment Numeric Compensation paid (BGN) Sick leave types Value Meaning Self_Sick Sick leave for the infected individual Family_Care Sick leave for caring for a sick family member varicella_bgr_population.csv Population denominators from the National Statistical Institute. Variables Variable Type Description year Integer Calendar year region Character Harmonised region region_bg Character Original Bulgarian region age_cat Character Age group gender Character Sex num_total Integer Total population num_city Integer Population living in cities num_villages Integer Population living in villages urbanisation Numeric Share of urban population The dataset includes a Total category representing the entire country. varicella_bgr_surveillance_cases.csv This dataset contains infectious disease surveillance notifications. Data are reported according to Ordinance No. 21. Variables Variable Type Description date Date Reporting month region Character Harmonised region region_bg Character Original Bulgarian region age_cat Character Age group gender Character Sex possible_num Integer Number of possible cases possible_rate Numeric Rate per population probable_num Integer Number of probable cases probable_rate Numeric Rate per population confirmed_num Integer Number of confirmed cases confirmed_rate Numeric Rate per population