Invasive pneumococcal disease in Latvia seven years after PCV10 introduction

Background. In 2009 in Latvia, invasive pneumococcal disease (IPD) became notifiable for physicians and in 2010 vaccination of infants with PCV7 commenced. In 2012 PCV10 vaccination was introduced. The objectives of our study were to evaluate trend of incidence and trend serotype distribution of IPD in Latvia and to investigate factors associated with death from IPD.
Methods. Laboratory confirmed IPD cases are passively notified to the Centre for Disease Prevention and Control of Latvia by laboratories and clinicians. We calculated incidence by age, sex, case fatality and trend in serotypes.
Results. From 2012 to 2018, 466 cases of IPD were reported, mean annual incidence 3.4/100,000. The notified incidence remained stable from 2012-2014 (2.7), peaked in 2015 (4.4) and fell to 3.9 in 2018. The highest mean annual IPD incidence was in infants (4.8) and in elderly (6). The highest mean annual incidence was reported in males (4.5) in comparison to females (2.4) (IR-1.8 95%CI 1.6-2.4). Case fatality was 19% (87/466) and 23% (37/162) in cases aged > =65 years. 90% (421/466) of isolates were serotyped. The proportion of PCV10 vaccine serotypes fell from 50% (20/40) in 2012 to 19% (14/74) in 2018 (chi2 test for trend =0.000). Since year 2017, PPV23nonPCV13 and Non-vaccine serotypes become more common. We detected PCV13 serotype (RR 2.04 95%CI 1.37-3.02), S.pneumoniae serotype 3 (RR 1. 91 95% CI 1.25-2.93) significantly associated with IPD death.
Conclusions. Surveillance data indicate evidence of serotype replacement. Surveillance evaluation should asses the representativeness of notification. Furthermore S. pneumoniae carriage study may be useful to characterise serotype circulation. Serotype 3 and age demonstrate independent and significant association with fatal IPD outcome.Key messagesIPD surveillance data analysis indicated evidence of serotype replacement with PPV23nonPCV13, NonVaccine serotypes. Serotype 19A becomes more common with significant increasing trend.Serotype 3 and age independently and significantly associated with fatal IPD outcome. S.pneumoniae carriage study would be very useful providing more evidence of characterizing serotypes circulation.