Blood culture contamination in a tertiary care hospital of Saudi Arabia

Discussion

Culturing of blood, though not the most sensitive technique, remains the current gold standard and clinically relevant laboratory diagnostic test for BSI, thereby guiding appropriate antimicrobial therapy. However, the contaminated blood cultures, leading to false positive results continue to intrigue the physicians and clinical microbiologists. To rule out the contaminants from positive blood cultures, the doctors rely on certain predisposing factors and the consistent clinical presentation of the patient. Further, certain skin-resident microorganism(s) such as Coagulase-negative Staphylococcus (Co-NS), Micrococcus, Alpha-hemolytic viridans group Streptococci, Propionibacterium acnes, Corynebacterium species (diptheroids) and Bacillus species have been reported as possible culture contaminants in earlier studies.4 The bacteria on skin cells are dislodged with venipuncture and have been considered to contribute to BCC. This has been corroborated in a recent trial, wherein an initial specimen diversion device was reported to coincide with a fall in BCC, presumably by flushing out the contaminating skin fragments and microorganisms in the initial volume of blood that was diverted and sequestered by the device.4 Bacillus species (excluding anthracis) and P. acnes have been isolated as co-contaminants with Corynebacterium species that being part of normal skin flora, do not cause invasive BSI except when present in indwelling devices such as joint prostheses, catheters, ports, vascular grafts, prosthetic heart valves, pacemakers.6 In another study, Co-NS (50%) and Propionibacterium species (19%) were found to be the most common cause of BCC.4

In our study, we found S. epidermidis as the most frequent contaminant. This is consistent with a recent study from Riyadh, Saudi Arabia wherein S. epidermidis was identified as the most prevalent contaminant (42.17%) among Co-NS isolates followed by S. hominis, S. capitis and S. hemolyticus.8 Min et al12 have reported S. epidermidis as the most frequently isolated contaminant (37%). We speculate that the biofilm forming capability of the skin microflora CoNS, such as S. epidermidis and S. capitis,13 may have contributed towards resistance to the bactericidal properties of antiseptics; as also reported in earlier studies.14 We found saprophytic skin-resident bacteria such as Bacillus species, Corynebacterium species, Diphtheroids and Streptococcus viridans alpha-hemolytic as contaminants in blood culture, as has also been reported by others.8 Ochrobactrum anthropi was identified as minor blood culture contaminant in our study, corroborating with earlier reports.15

Several factors have been attributed to contamination in blood cultures such as following unhygienic and improper aseptic techniques for sterilizing skin while drawing blood, particularly by untrained phlebotomists, use of existing indwelling or invasive devices like ports or intravenous catheters rather than peripheral venipuncture for obtaining blood.6,16 Occasionally, the patients from whom blood is drawn for culturing are usually very sick, and concurrently receiving antibiotics and fluids, resulting in drawing of blood from intravenous accesses. Trained and competent nurses have been reported to result in fewer contaminated blood cultures.9 Recent studies suggest that the technique employed to disinfect the venipuncture site followed by a few minutes of drying time impacts the BCC rate rather than the antiseptic.2,17 However, the effectiveness of alcoholic solution prior to BC sampling has also been reported in reducing contamination rate.3 The back-and-forth friction method of applying the disinfectant to scrub the area prior to drawing of blood, has been reported to be more beneficial than the concentric method, as it cleanses the upper dermal layers of the skin, removing most of the commensal bacterial load.18 Use of sterile blood culture systems such as BD Vacutainer, Push Button BC Collection kit, BacT/ALERT adapter, cap and insert (Biomérieux) or BacT/ALERT® BC bottles have been reported to significantly lower the contamination rate.19 Inadequate volumes of blood for culture and the sequential drawing of blood when it is to be used for multiple laboratory tests, also adversely impacts the contamination rate.6

Other exogenous risk factors contributing to neonatal sepsis and BCC that have been identified in premature and low birth weight infants, include the increased length of hospitalization in neonatal ICU, surgical procedures, parenteral nutrition, and use of invasive devices such as mechanical ventilation and central venous catheters.20 Elderly patients have been reported to have more likelihood of BCC due to difficulty in accessing the poorly accessible veins.11 In our study, none of these contributing factors majorly impacted the contamination rate except the age and gender of the patients. We found that contamination rate was generally higher in the males than the females. The cultures from elderly patients in the age group of 60-80 years were more vulnerable to contamination. Our finding is in line with those reporting an association between increasing age and BCC rate.10

In our study, the patient’s venipuncture site was disinfected with alcohol swab and then blood drawn as the nurse inserted needle after palpating repeatedly with gloved hands to look for prominent veins. The factors contributing to the higher-than-desired BCC rate in our study were identified as improper aseptic techniques (such as allowing contact time of 1-2 min for antiseptic solution, prior to venipuncture) followed by the less competent nurses during August-October, the Hajj season in the year 2017, as most of senior staff were on vacation. We also observed higher BCC rate from Emergency, ICU, and medical wards during December to January and March to April. The favorable weather and children’s vacation may have favored high turnover of visitors for Umrah during these periods. This is in concordance with the reports indicating higher BCC rates during periods of increased crowding, wherein lapses in proper collection techniques by the health care workers have been suggested as contributory factors.6 The higher BCC rate in the medical ward is also related to the number and health status of the patients as elderly with comorbidities are admitted there and it is difficult to draw blood from them. Another study indicated BCC rates as high as 10-12% from overcrowded emergency department.21 We infer from our study that efforts should be directed towards mitigating the BCC rate during the Hajj and Umrah season, when there is high influx of visitors from around the world, may be, by more adequate staffing of trained nurses and adopting proper aseptic procedures.

The BCC rate in our one-year study (6.58%) was slightly lower than that reported by others. A contamination rate of 10.4% has been recorded in a one-year study from Nigeria.22 Another study in AlQatif, Saudi Arabia recorded 8.1% monthly BCC rates that dropped to 5.2% post-intervention.9 Blood culture contamination has been reported to be reduced from 6.37% to 4.34% in a Malaysian hospital post-intervention.23 The higher rates of contamination have also been ascribed to the newer, continuous monitoring blood culture systems, which detect microbial growth more efficiently and quickly that were missed in the earlier conventional methods. The new molecular techniques such as multiplex PCR-based assays and nucleic acid amplification test (NAAT) also facilitate rapid identification of bacteria in positive BC bottles.24 Nonetheless, our study implicates that efforts should be focused to mitigate the escalated false positive blood culture rates to the desired level (<3%) by deploying more trained staff. The nurses should be directed to focus on strict antiseptic guidelines instead of drawing blood for culture in a haste. The skin should be properly disinfected prior to venipuncture, and drawing blood from indwelling devices such as catheters should be avoided. The tops (rubber diaphragm) of blood culture bottles and the catheter hub/port diaphragm of intravascular devices should be properly disinfected with 70% ethanol or isopropyl alcohol.2

Efforts towards waning the BCC rates could significantly lower the period of hospital stays and administration of unnecessary antibiotics, and hence curtail the cost, and curb the mounting menace of drug resistance. Ours is the first study on the BCC rates in a tertiary care hospital in Madina, Saudi Arabia. Blood culture contamination rate should be regularly monitored in all the hospitals and the hospital staff briefed about the surveillance data. This would help to dampen contamination rates, reduce emergence of drug resistant strains, and shorten the period of hospitalization and hence economic burden.