October 2000
BARDSTOWN, Ky. - Acute conjunctivitis is common during childhood, and most pediatricians treat the condition empirically with topical antimicrobials.
While this is still the most practical course, several factors should be considered when deciding which antimicrobial to prescribe, according to results of a study recently published in Antimicrobial Agents and Chemotherapy.
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Researchers sequentially cultured a sample of 250 previously healthy children with acute conjunctivitis from January 1997 through March 1998. Most children were younger than 2, and physicians primarily cultured children with obvious purulent discharge. They diagnosed acute conjunctivitis by signs of conjunctival inflammation. Children were also assessed for signs of acute otitis media (AOM) and rhinorrhea. Clinicians diagnosed AOM when marked hyperemia, full or bulging tympanic membrane, purulent effusion or air-fluid levels or discoloration with yellow, white or green opacification were present.
"Haemophilus influenzae is still the No. 1 pathogen of acute bacterial conjunctivitis," said Stan L. Block, MD, of Kentucky Pediatric Research Inc. here. H. influenzae accounted for 106 (42%) isolates in the study.
Researchers detected ß-lactamase production in 60 (69%) of 87 confirmed H. influenzaestrains. The prevalence of b-lactamase producing H. influenzae solated from children has increased from 16% in the nasopharynx during the mid-1980s to 44% in the late 1980s to 69% currently in acute conjunctivitis. However, researchers found that b-lactamase production among H. influenzae strains had no effect on antimicrobial susceptibility to available topical agents.
Seventy-five (30%) Streptococcus pneumoniae isolates were initially identified on blood agar plates, and 21 (28%) of these were resistant by oxacillin disc testing. Broth microdilution of 65 viable strains showed that 17 (26%) were resistant, four (7%) had intermediate resistance, and 44 (68%) were susceptible. Both pathogens were recovered from 10 (4%) children.
Ninety-seven (39%) children were diagnosed with conjunctivitis and AOM. H. influenzae (57%) accounted for most of these cases, followed by penicillin-susceptible S. pneumoniae 18%) and penicillin-nonsusceptible S. pneumoniae 8%).
Eighty-six percent of children with conjunctivitis had purulent discharge, and 53% had erythema of the conjunctiva. Children with bacterial conjunctivitis were more likely to have rhinorrhea.
Because H. influenzae is still the primary pathogen of acute conjunctivitis, researchers said that topical antibiotics such as polymyxin combinations or other antibiotics more active against H. influenzae are good choices for initial therapy. However, most strains of penicillin-susceptible and penicillin-nonsusceptible S. pneumoniae had resistance to polymyxin B, neomycin or combination polymyxin B-neomycin (see tables).
Researchers found tetracycline, chloramphenicol, erythromycin, gentamicin and tobramycin (TobraDex, Alcon) to be intermediately effective.
Aminoglycosides are best avoided when treating bacterial conjunctivitis, Block said. "Those are commonly used topicals." However, "their coverage is marginal." H. influenzae and S. pneumoniae "have some degree of resistance to the aminoglycosides."
Sulfamethoxazole is another poor choice for treating conjunctivitis and sulfonamides "will probably have no effectiveness whatsoever for respiratory tract infection prevention or treatment," Block said.
Additionally, hypersensitivity reactions and the irritating nature of sulfonamides are other reasons that their future use - either prophylactically for AOM or for treatment of conjunctivitis - should be discouraged.
Penicillin-nonsusceptible S. pneumoniae should be suspected as the causative pathogen when children older than 2 months fail to respond to initial topical antibiotic therapy.
"Nobody really thinks about it being a pathogen there," Block said. "But if a child does not respond after one or two courses of reasonably effective topical antibiotics, then we need to seriously consider resistant S. pneumoniae as being the culprit."
Researchers found topical ciprofloxacin (Ciloxan, Alcon) and topical ofloxacin (Ocuflox, Allergan) to be the most active against both S. pneumoniae and H. influenzae and to be particularly active against penicillin-nonsusceptible S. pneumoniae. Either may be used to treat acute conjunctivitis in children older than 12 months. A standard aerobic culture should also be considered, Block suggested.
Infants older than 2 weeks in lower risk populations may be given empiric therapy targeting common aerobic pathogens, according to researchers. However, if symptoms do not improve or if they recur within a week, culturing for aerobic pathogens, testing for Chlamydia trachomatis and prescribing both topical and oral erythromycin should be considered.
When a child is concurrently diagnosed with AOM, third-generation cephalosporins or amoxicillin-clavulanate (Augmentin, SmithKline Beecham) or other b-lactamase stable oral antibiotics should be added.
"When you see a child with concomitant conjunctivitis/otitis syndrome, you really need to initially cover for ß-lactamase-producing H. influenzae and not use amoxicillin in this scenario," Block said.
| Susceptibilities for H. influenzae
Isolates |
||||
|---|---|---|---|---|
| The following are antimicrobial
susceptibility data from in vitro studies of children with acute bacterial
conjunctivitis, from 1997-1998. Percentages are minimum inhibitory
concentrations (µg/mL). |
||||
| Antibiotic | ß-Lactamase Non-Producing Strains | ß-Lactamase-Producing Strains | ||
| 50% | 90% | 50% | 90% | |
| Ciprofloxacin | .0.008 | 0.016 | 0.008 | 0.016 |
| Gentamicin | 4 | 8 | 4 | 8 |
| Polymyxin | ||||
| B-trimethoprim* | 0 .5/0.4 | 1/0.8 | 0.5/0.4 | 1/0.8 |
| Sulfamethoxazole | 128 | 256 | 128 | 256 |
| Tobramycin | 4 | 8 | 4 | 8 |
| *Polymyxin B is expressed in µg/mL. The activity of the formulation used was 7,500 IU/mg. | ||||
| Source: Stan L. Block, MD | ||||
| Susceptibilities for S. pneumoniae
Isolates |
||||
|---|---|---|---|---|
| The following are antimicrobial
susceptibility data from in vitro studies of children with acute bacterial
conjunctivitis, from 1997-1998. Percentages are minimum inhibitory
concentrations (µg/mL). |
||||
| Antibiotic | ß-Lactamase Non-Producing Strains | ß-Lactamase-Producing Strains | ||
| 50% | 90% | 50% | 90% | |
| Ciprofloxacin | .0.5 | 1 | 1 | 1 |
| Gentamicin | 8 | 16 | 8 | 16 |
| Polymyxin | ||||
| B-trimethoprim* | 4.1/3.3 | 16.3/13 | 280/210 | 520/430 |
| Sulfamethoxazole | 32 | >256 | 256 | >256 |
| Tobramycin | 16 | 32 | 16 | 64 |
| *Polymyxin B is expressed in µg/mL. The activity of the formulation used was 7,500 IU/mg. | ||||
| Source: Stan L. Block, MD | ||||
For more information:
- Block SL, Hedrick J, Tyler R, et al. Increasing bacterial resistance in pediatric acute conjunctivitis. Antimicrob Agents Chemother. 2000; 44(6):1650-1654.
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