Our study confirms a high carriage of potential pathogens, many of which are antibiotic resistant, from NP and blood culture isolates in HIV-infected children. The majority of organisms from both NP and blood were resistant to TMP-SMX and other antibiotics commonly used for community-acquired infection. A disturbing finding was the high prevalence of MRSA and ESBL-producing Enterobacteriaceae from both sites.
The demographic features of HIV-infected children are similar to those described previously at the Tygerberg Family clinic where the majority were under two years of age, had moderate or severe immunosuppression and symptomatic HIV disease . Mortality has been described elsewhere and was not analyzed further as it may have been affected by multiple factors beyond the scope of this report . The significant difference in age of subjects stratified by TMP-SMX exposure probably reflects utilization of the public health service. Subjects entered the study from January 2003, as the Vertical Transmission Prevention program was gradually being introduced in the Western Cape. Consequently, many of the older infants and children were only identified through knowledge of their parents' HIV status, or when presenting with clinical disease suggestive of HIV. Those never exposed to TMP-SMX were significantly younger than those already on TMP-SMX. Those previously on the drug but not receiving it at baseline were older, possibly reflecting poor retention in the public health system.
Colonization by S. pneumoniae, H. influenzae and M. catarrhalis is well documented in early childhood . Approximately 50% of children carry S. pneumoniae at two years of age, declining to 20% by 7 years. Below 7 years of age 40% of immunocompetent children in developed countries carry M. catarrhalis and 30% H. influenzae . Socioeconomic factors such as housing, overcrowding, poor hygiene, access to health care and daycare are major determinants of colonization. For example, in Australia, Aboriginal children are colonized with M. catarrhalis, H. influenzae and S. pneumoniae by 20 days of age, whereas non-Aboriginal children acquire these organisms after 200 days of age . Increased numbers of colonizing faecal organisms such as Enterobacteriaceae and Pseudomonas have been found in malnourished infants and children from resource-poor settings in the pre-HIV era [7, 8]. A recent comparative community-based study of children aged between 4 months and 5 years, showed more frequent carriage of Gram-negative enteric pathogens in Brazilian (50%) and Angolan (57%) than Dutch children (4%) .
Studies on NP S. pneumoniae in HIV-infected adults and children from developed countries showed similar carriage rates to uninfected subjects [27, 3, 28]. In Kenya, Rusen et al found no increased NP S. pneumoniae colonization in asymptomatic HIV-infected infants (20%) compared to seronegative controls (22%) .
In our study, colonization by Enterobacteriaceae was associated with age below a year and advanced HIV disease. S. aureus was linked to CD4 depletion and Gram-negative respiratory organisms to absence of CD4 depletion. High carriage rates of S. aureus and possible relationship with invasive disease, has been noted in HIV-infected adults [29, 30]. In a study from the Western Cape, comparing community acquired pneumonia in HIV-infected and uninfected infants, Zar et al found a higher rate of S. aureus in nasopharyngeal aspirates and invasive disease, linking this finding to TMP-SMX prophylaxis in HIV-positive children . Similarly, in a recent survey of children hospitalized with severe pneumonia in Kwazulu-Natal, South Africa, HIV-infected children were significantly more likely to be colonized with S. aureus (31%) than HIV-uninfected children (13.8%) .
TMP-SMX resistance occurs commonly in children. For example in a recent survey of H. influenzae colonization in daycare attendees in Brazil, 46% were resistant to TMP-SMX and 10% had multidrug resistance . Although not reported, HIV prevalence was likely to be extremely low. Abdel-Haq showed that both young age and TMP-SMX prophylaxis were risk factors for NP colonization with multiply resistant S. pneumoniae in immunocompromised and immunocompetent children from Detroit, USA .
Antibiotic resistance was extremely common in our study. Between 80 – 90% of most pathogens (except for M catarrhalis) were resistant to TMP-SMX. Almost 80% of S. aureus were methicillin-resistant and 50% of Enterobacteriaceae had ESBL production. The majority of children had advanced disease and frequent contact with both in- and outpatient hospital facilities. High prevalence of antibiotic resistance has already been described in malnourished children with pneumonia and also in children with hospital-associated bacterial infection [32, 33]. We did not record TMP-SMX usage or frequency of healthcare utilization in other family members, but speculate that both were likely to be high, as other family members are also likely to be HIV-infected. The children enrolled in the study come from poor socio-economic conditions where overcrowding and spread of antibiotic resistant pathogens in homes are likely. As we did not link previous hospitalization with antibiotic resistance in NP organisms, we speculate that antibiotic resistance is well established in homes of study subjects and possibly in the communities, as well. As evidence of this, TMP-SMX resistance was significantly higher in S. pneumoniae in subjects without a history of hospitalization. Also, even though we found significantly more MRSA in children on TMP-SMX at baseline, 70% of those not on TMP-SMX also had MRSA, supporting the contention that the organism is well established in the homes of the infants. A major limitation of our study is that we did not document NP colonization in HIV-uninfected children from the same communities or within the household of our subjects. We plan to address these issues.
Colonization with antibiotic resistant organisms has been noted in surveys of African children and adults. In 1997, Woolfson described S. pneumoniae in 72% of 260 Zambian school children < 6 years of age. Antibacterial resistance occurred in 34.1% of isolates; intermediate resistance to penicillin occurred in 14.3% and to TMP-SMX in 12.7% . In the Kenyan study from 1997, Rusen et al documented that 60% of S. pneumoniae isolates had intermediate resistance to penicillin . Both studies preceded the widespread use of TMP-SMX for chemoprophylaxis in HIV-infected infants . MRSA has been found more commonly in HIV-infected than uninfected children in Kwazulu-Natal, South Africa .
The incidence of bacteremia (9.4%) is higher that from a survey in the pre-HIV era. In a study of hospitalized children at Tygerberg Hospital in 1989, 2% had bacteremia, the most frequent isolates being S. pneumoniae and S. aureus. In community-acquired infections, pathogens were also sensitive to first line antibiotics . In a study of infants with severe lower respiratory tract infection in Soweto, S. pneumoniae and S. aureus from bacteremic infants showed significantly higher levels of penicillin (54 versus 23%) and methicillin resistance (60% versus 0%) respectively in HIV-infected than uninfected infants .
Community-associated infection due to MRSA is an emerging problem in children from developed countries [37, 38]. In contrast, community-associated infection due to ESBL-producing organisms is well documented in adults, but not yet in children .
The colonizing NP flora and high level of antibiotic resistance for Enterobacteriaceae and S. aureus suggest that empiric antibiotic treatment should be adapted to cover MRSA and ESBL-producing Enterobacteriaceae. Also, amikacin is a more appropriate aminoglycoside than gentamicin for severely ill HIV-infected children in our region. A limitation of our study, however, is that we did not distinguish between community and hospital acquired bacteremia or nasopharyngeal colonization. To our knowledge, this is the first documentation of ESBL-producing Enterobacteriaceae causing bacteremia or colonizing the nasopharynx in HIV-infected children.