Changes in Invasive Pneumococcal Disease among HIV-Infected Adults Living in the Era of Childhood Pneumococcal Immunization

Increased Prevalence of Pediatric Pneumococcal Serotypes in Elderly Adults:

With the introduction of the 23-valent pneumococcal vaccine in adults and the 7-valent conjugated vaccine in children a significant reduction of pneumococcal disease in the developed world has ensued. The 2 vaccines contain some different serotypes characteristic of each age group's prevalence. Feikin et al (1) recently reported an increased prevalence of pediatric serotypes 6B, 9V, 14, 19F and 23F in elderly adults (>65 years). From 1998-1999 invasive pneumococcal disease described as isolation of Streptococcus pneumoniae from a normally sterile site, such as blood or CSF was studied in 2987 isolates. The data showed that the percentage of adults with pediatric serotypes recently rose from 33% in persons aged 35-64 to 44% in patients 65-74, 47% in those 75-84 and to 51% of patients over 85 years.

Laxau et al (2) described a reduction of invasive pneumococcal disease among adults age 50 years or older and noted that the incidence of disease caused by the 7 conjugate vaccine serotypes declined 55%. Most recently Flannery et al (3) also noted an overall decrease among HIV-infected adults 18 to 64 years of age living with AIDS since the introduction of the pediatric conjugate vaccine.

We have since 1998 serotyped all pneumococci isolated from blood, CNS, sinuses and middle ear of 34 adults over 30 years of age seen in the clinical practice of a single infectious diseases specialist to initially evaluate what percentage of those infected were immunized with 23-valent vaccine. Those data revealed that only a single person with pneumococcal disease had previously been immunized. More recently we have retrospectively examined the serotypes in these same patients and found that 4 were serotype 6B, 2 were serotype 9V, 1 was serotype 14, 6 were 19F, and 8 were 23F. In total, 21 patients of 34 (62%) were infected by these pediatric serotypes, slightly higher than 55% noted by Feiken in the his study. However, in addition to the above we also found serotype 18C in 3 patients but did not isolate serotype 4 in anyone. Thus 6 of 7 pediatric serotypes were isolated in 24 0f 34 patients (70%) in our study group. In the remaining 10 patients, 5 were 11, 2 were 29 and 1 each were 3, 16 and 44. Thus, 3 of 34 (11%) serotypes isolated in our group of patients were not included in either the 23- or 7- valent vaccines.

Twenty six out of 34 patients (76%) were over 65 years and 23 (65%) were over 75 years of age and 9 (30%) were older than 85 years. Seven of 9 patients over the age of 85 (71%) grew out pediatric serotypes, while 16 of 23 (69%) over 75 and 17 of 26 (65%) over 65 years of age revealed pediatric serotypes. Only 2 patients died as a result of pneumococcal infection.

While our numbers are small, and the data reflect a single physician's experience, they confirm Feikin's findings that elderly individuals are more susceptible to pediatric serotypes of Streptococcus pneumoniae. These findings stand in contrast to those of Lexau (2) and Flannery (3) who both showed a decrease of 7 conjugate vaccine serotypes of 55% and 62% respectively in the elderly and those with HIV infection. Both authors note an increase an increase in non- conjugate vaccine containing strains which amounted to only 11% in our series.

Since, only a single patient of 34 in the group received 23-valent pneumococcal vaccine, it would imply that failing natural immunity leads to recurrence of pediatric strains of pneumococci in the elderly and that pediatric conjugate vaccine serotypes continue to be the dominant organisms.

REFERENCES

1. Feiken DR, Klugman KP, Facklam RR, Zell ER,Schuchat A, Whitney CG, for the\Active Bacterial Core surveillance/Emerging Infections Program. Increased prevalence of pediatric pneumococcal serotypes in elderly adults. Clin Infect Dis 2005;41:461-7. 2. Lexau CA, Lynfield R, Danila R, et al. Changing epidemiology of invasive pneumococcal disease among older adults in the era of peditaric pneumococcal conjugate vaccine. JAMA 2005;294:2043-51. 3. Flannery B, Hefferman RT, Harrison LH, et al. Changes in invasive pneumococcal disease among HIV- infected adults living in the era of childhood pneumococcal immunization. Ann Intern Med 2006;144:1- 9.

Lawrence A. Cone MD, FACP, 1,2

Ariella E. Morrow 1,2

Radhika Gade-Andavolu, PhD 2

Eisenhower Medical Center, 1

Genetic Research Institute of the Desert 2

Rancho Mirage, CA 92270

Conflict of Interest:

None declared