Invasive Pneumococcal Disease in New Zealand, 2010

type most frequently reported to have increased. 12,14 Increases in type 19A disease have beenof particular concern as this serotype is often associated with antibiotic resistance. 14,15 Therehave been recent reports of increasing rates of resistance among invasive serotype 19Aisolates associated with shifts in the genetic structure of the isolates and the expansion ofparticular resistant clonal complexes. 16 As yet there have not been any significant increasesin rates of type 19A IPD in New Zealand since the introduction of PCV-7 but there was anon-significant increase in the rate of 19A disease in those ≥65 years old between 2009 and2010: from 1.6 to 3.7 cases per 100 000. In addition, to date, invasive serotype 19A isolatesin this country are not especially associated with resistance and there have been no significantchanges in resistance among this type over the last 10 years.IPD cases due to the non-PCV-7 serotype 1 have increased since 2007, but appear to havepeaked in 2009 with the case numbers in 2010 (77) being less than half those in 2009 (153).These serotype 1 cases have been strongly associated with IPD in Māori and Pacific schoolagechildren and young adults. However, this increase in serotype 1 disease is unlikely to bea result of serotype replacement following the introduction of PCV-7 since the increase inthis type commenced before the introduction of the vaccine and appears to now be waning.In addition, it has mainly been associated with age-groups who are not eligible for PCV-7vaccination. This pattern of serotype 1 disease fits with that observed globally for thisserotype, that is, outbreaks that occurring cyclically every few years. 17Pneumococcal serotype 6C was first described in 2007. 18 Until 2010, the serotyping methodsused at ESR resulted in both serotypes 6A and 6C being designated as type 6A.Retrospective work has commenced on re-typing invasive pneumococcal isolates designatedas 6A prior to 2010 to differentiate types 6A and 6C. Correct categorisation of these isolateswill enable more precise monitoring of any cross-serogroup protection conferred by theserotype 6B antigen included in PCV-7 and PCV-10. The epidemiology of IPD in othercountries suggests that PCV-7 use has resulted in a reduction in type 6A, but not 6C, IPD. 19In 2010, most (79.4%) of the IPD cases in infants who had received ≥1 dose of PCV-7 weredue to a non-PCV-7 type. Among the seven cases who had received ≥1 dose of PCV-7 andhad disease due to a PCV-7 type, five had serotype 19F disease, one had type 6B disease andone had type 14 disease. Serotypes 19F and 6B were found to be the most common typesassociated with vaccine breakthrough cases in a United States study. 20As most resistant invasive pneumococci belong to one of the serotypes included in PCV-7, adecrease in IPD caused by vaccine types would be expected, and has been observed in othercountries, to have the concomitant effect of reducing the incidence of IPD caused by resistantpneumococci. 21 Although there was a decrease in penicillin and cefotaxime resistancebetween 2008 and 2009, there was no further decrease between 2009 and 2010. However,there is no indication that resistance is increasing in non-PCV-7 serotypes in this country,with PCV-7 types still accounting for over 80% of the penicillin and cefotaxime resistance in2010.We noted last year that nearly one-tenth (59/697) of the IPD cases notified in 2009 did notinclude evidence that they met the case definition. 7 This improved considerably in 2010 withno cases notified on the basis of pneumococci or pneumococcal DNA isolated from ordetected in a site that was unequivocally not a normally sterile site.Invasive pneumococcal disease 23 September 2011in NZ, 2010