RESUMEN
BACKGROUND: We describe how rates of two frequently occurring notifiable diseases-diphtheria and scarlet fever-varied between regions of The Netherlands in the early twentieth century, and identify potential factors underlying this variation. METHODS: Digitized weekly mandatory notification data for 1905-1925, municipality level, were aggregated into 27 'spatial units' defined by unique combinations of province and population density category (high: more than 4500; mid : 1250-4500; low: less than 1250 inhabitants km-2). Generalized additive regression models were fitted to estimate the associations between notification rates and population density, infant mortality rate and household income, while adjusting for temporal trends per spatial unit. RESULTS: Annual per capita notification rates for both diphtheria and scarlet fever tended to rise from the beginning of the period 1905-1925 until peaking around 1918/1919. Adjusted diphtheria notification rates were higher for high- and mid- compared with low-density municipalities (by 71.6 cases per 100 000, 95% confidence interval (CI) : 52.7-90.5; 39.0/100 k, 95% CI : 24.7-53.3, respectively). Scarlet fever showed similar associations with population density (35.7 cases per 100 000, 95% CI : 9.4-62.0; 21.4/100 k, 95% CI: 1.5-41.3). CONCLUSIONS: There was considerable spatial variation in notification rates for both diseases in early twentieth century Netherlands, which could partly be explained by factors capturing variation in living conditions and socio-economic circumstances. These findings aid understanding of contemporary respiratory infection transmission.
RESUMEN
BACKGROUND: Diphtheria is a severe respiratory or cutaneous infectious disease, caused by exotoxin producing Corynebacterium diphtheriae, C. ulcerans and C. pseudotuberculosis. Diphtheria is once again prevalent due to breakdown of immunisation programmes, social disruption and unrest. AIM: This study describes the notified diphtheria cases in the Netherlands between 2000-2021 and isolates that were sent to the National Institute for Public Health and the Environment (RIVM). METHODS: File investigation was performed including all notified cases and isolates of C. diphtheriae, C. ulcerans and C. pseudotuberculosis that were tested for toxin production using a toxin-PCR and Elek test. An exploratory review was performed to understand transmission in populations with a high vaccination uptake. RESULTS: Eighteen diphtheria notifications were made with confirmed toxigenic C. diphtheriae (n = 9) or ulcerans (n = 9) between 2000 and 2021. Seventeen (94.4%) presented with a cutaneous infection. All cases with a suspected source abroad (n = 8) concerned infection with C. diphtheriae. In contrast, 9/10 cases infected in the Netherlands were caused by C. ulcerans, a zoonosis. Secondary transmission was not reported. Isolates of C. ulcerans sent to the RIVM produced more often the diphtheria exotoxin (11/31; 35%) than C. diphtheriae (7/89; 7.9%). CONCLUSION: Both human-to-human transmission of C. diphtheriae and animal-to-human transmission of C. ulcerans rarely occurs in the Netherlands. Cases mainly present with a cutaneous infection. Travel-related cases remain a risk for transmission to populations with low vaccination coverage, highlighting the importance of immunization and diphtheria control measures.
