Statistical analyses
Data was analysed using Stata 16.1 (College Station, Tx, USA). The association between sensorineural hearing loss and possible risk factors were investigated using uni- and multivariate logistic regression. Variables showing a substantial association with the outcome in the univariate analysis were kept in the multivariate analysis. To evaluate the effect of age, patients were divided into four age groups; children (0-11 years), teenagers (12-21 years), adults of working age (22-65 years), and elderly (over 65 years).
In a substantial number of patients (n=68), hearing tests were not performed. In order not to overestimate the prevalence of hearing loss by only including patients with hearing tests, data for all patients were used, making the conservative assumption that patients lacking hearing tests had normal hearing.
Results
Initially, 556 patients were identified. After applying exclusion criteria, 187 patients remained (Figure 1), 106 of whom were men. The age distribution is shown in Table 1. Hearing tests were available in 119 cases, 107 of which were pure tone audiometries. Hearing loss was diagnosed in 81 patients, in 13 cases unilaterally, and was more common in adults and elderly (Table 1). Three patients had bilateral severe hearing loss, and an additional 13 had unilateral severe hearing loss. Of the 105 patients where data for 6 and 8 kHz were available, hearing thresholds >40 dB on these frequencies occurred frequently in adult patients, however, never in children or teenagers (Table1). The most commonly identified bacteria were S. pneumoniae (58%) andN. meningitidis (12%) (Table 2).
In the univariate analysis, there was no evidence of a correlation between gender and hearing loss, however, there was strong evidence of adult and elderly patients having greatly increased odds of hearing loss (OR=7.3, p=0.01 and OR=8.4, p=0.007).
There was also evidence that patients with pneumococcal infection had increased odds of hearing loss (OR=4.1, p<0.001). On the other hand, patients with meningococcal infections had decreased odds of hearing loss (OR=0.2, p=0.009). There was also evidence for an association between hearing loss and concurrent AOM (OR=3.3, p<0.001).
Age, concurrent AOM and presence of S. pneumoniae /N. meningitidis was kept in the multivariate analysis (Table 3). There was still strong evidence that age was a risk factor for hearing loss. Patients with concurrent AOM had twice the odds of hearing loss, and for those with pneumococcal infection, the odds increased 3.6-fold. In the multivariate analysis, no association was seen between meningococcal infection and hearing loss.