The present study is the first surveillance study conducted in Greece at nation-wide level in the pre-vaccination era, with representative samples per geographical region, according to the age-specific population distribution in the most recent records of the National Registry in March 2001 [12
Carriage rates in the present study varied significantly with age, period of sampling and the geographic area visited. This significant trend differentiation stresses the importance of sequential sampling in a specific area and multifocal sampling at a specific time-point, as useful tools in the epidemiological studies of resistance. It must be noted that regional differences in carriage rates did not affect resistance/nonsusceptibility rates. Resistance rates differed among different regions. This difference per region renders the results of a multicenter study even more valuable, as it may predict similar trends in the clinical isolates [13
]. In the present study serotyping was performed only in the resistant strain population. Thus, the association of specific serotypes with specific resistance patterns cannot be accurately performed and regional variability in resistance rates for penicillin and erythromycin in relation to serotype distribution requires caution.
One of the risk factors amenable to intervention for carrying a resistant or a non-susceptible pneumococcal strain in the nasopharynx for a healthy preschool child was the use of antibiotics in the month preceding sampling. Additionally, antibiotic use was related to the isolation of combined penicillin-erythromycin resistant, as well as multiresistant pneumococcal strains Numerous studies [14
] have pointed out antibiotic consumption as a very strong pressure factor for the development of resistance, irrespective of ecological setting (individuals-community). Chung et al
] have recently shown that prescription of amoxicillin doubled the risk of recovery of β lactamase producing Haemophilus influenzae
strains. Although this effect was transitory at an individual level (2 weeks), it was sufficient to sustain a high level of antibiotic resistance in the study population.
Acute otitis media was the most frequent infection for which a child received antibiotics in our study. Nonetheless, a similar proportion of children (approx. 30%) consumed antibiotics for infections which seemed to be of viral cause by all descriptions in the questionnaire used. It must be stressed that acute otitis media does not always require prompt administration of antibiotics, as it may be of viral origin in certain cases. In Finland Palmu et al
recorded negative cultures of middle ear fluid in approximately 35% of children with acute otitis media in 2004 [18
]. Moreover, a wait-and-see approach to acute otitis media treatment in the paediatric population seems to reduce antibiotic consumption and subsequent resistance without jeopardizing children's safety and well-being [19
Approximately 90% of the prescriptions originated from practicing physicians in the community, while in the remaining 10% of cases, parents had access to antibiotics without doctor's prescription, although this is not abiding by antibiotics policy law [20
]. As demonstrated by Guillemot et al
], intensive educational strategies, targeting to optimize antibiotic use both in terms of indications and of dose/duration of administration, significantly reduced the colonization with penicillin non-susceptible pneumococci in areas with high prevalence of resistance.
The heptavalent pneumococcal vaccination (PCV7) covered 71.32% of resistant strains in total in the present study. The most prevalent serotypes in our population carried the heavier burden of antibiotic resistance. Implementation of the heptavalent vaccine has been shown to be highly efficacious in decreasing the incidence of vaccine-type antibiotic-resistant strains in disease and colonization [5
]. A study by Grivea et al
], at a regional level in Thessaly, Central Greece between 2005–2007, showed that increasing rates of PCV7 population coverage was associated with a reduction in colonization by PCV7-related serotypes in vaccinated (from 33% to 8.6%, P
< 0.001) and unvaccinated children (from 36% to 17%, P
= 0.05). Moreover, a decrease in the rate of highly penicillin resistant pneumococcal isolates was recorded only in vaccinated children (from 11% to 0.6%, P
= 0.001), whereas rates for penicillin intermediate strains were not affected.
In a community setting of high antibiotic consumption, Frazao et al
] showed that PCV7 vaccination was successful in the reduction of vaccine related strains, but it did not change the frequency of nasopharyngeal carriage of drug resistant pneumococci, implying the crucial role of antibiotic consumption on the serotype replacement phenomenon by drug-resistant non-vaccine related pneumococcal strains.
To reduce antibiotic resistance in the community, reducing unnecessary antibiotic prescriptions combined with the implementation of the heptavalent conjugate pneumococcal vaccine are probably two of the most efficient strategies. In a large scale prospective study in France from 2001 to 2005 in children presenting with acute otitis media, Cohen et al
] showed that unvaccinated children who had received antibiotics within the last three months had a 4-fold greater risk of carrying a penicillin resistant strain than vaccinated children who had not received antibiotics. Moreover, vaccination reduced the antibiotic consumption from 51.6% to 38.5%, as well as the risk for a child to carry a penicillin resistant pneumococcal strain from 15% to 3%.