CDC’s Animal and Mathematical Models

September 15, 2017

Animal Model
Grabowsky and colleagues utilized an animal model to assess the degree of contamination from a Ped-O-Jet injector. Two sets of in vitro tests were conducted to measure the frequency and volume of Hepatitis B surface antigen. The first test measured the degree of contamination when the gun was used according to the manufacturers recommendations. The second test measured the degree of contamination when the nozzle was wiped after administering an injection. These tests were similar to previous jet injector experiments conducted by CDC in 1977 and 1986, thanks in part to Walter Bond who served within all three experiments.

First Test
Within the first test, the researchers assessed whether after firing the Ped-O-Jet if the Hepatitis B surface antigen (HBsAg) would be sucked into the nozzle orifice and contaminate the next dosage. Detection of HBsAg would be indicative of Hepatitis B transmission.

For this experiment, the underside of a rabbit was shaved five days prior to testing. Upon the day of the experiment the rabbit was euthanized and 0.025 milliliters of HBsAg serum was placed upon the shaved skin of the rabbit. A sterile Ped-O-Jet administered a 0.5 milliliters injection to the now HBsAg-contaminated underbelly of the rabbit. Following the injection, the gun was held in place for 2 to 3 seconds, per manufacturer’s instructions. The Ped-O-Jet was then fired once into five separate 1 dram vials. The ejected fluid within each of the five vials was tested for HBsAg using Radioimmunoassay Ausria II. The test was repeated ten times creating a total of 50 samples. Every time the test was repeated the Ped-O-Jet was sterilized through autoclaving (Grabowsky et al., 1994).

The Ausria II Radioimmunoassay to detect Hepatitis B surface antigen was the same radioimmunoassay used within the 1977 investigation. It remains unclear why the researchers did not use newer, more sensitive radioimmunoassays able to detect far lower levels of HBsAg. The fact that Ausria II was used again was likely the decision of Walter Bond who served within both investigations of the Ped-O-Jet.

Nonetheless, the results found the ejected fluid of the next shot fired was positive for HBsAg in 19 out of 50 (38%) of the samples. Within these contaminated samples, the average volume of blood detected in the ejectate was 0.118 microliters (range, 0.023 uL – 0.417 uL) (Grabowsky et al., 1994). The exterior nozzle of the Ped-O-Jet was positive for HBsAg in 8 out of 10 (80%) of the samples. Yet the interior of the nozzle was negative (0 out of 10) for HBsAg contamination (Weniger, 2003). This data demonstrated significant contamination.

To put this into perspective, lets convert these figures into picoliters which is the smallest estimated unit for transferring blood-borne pathogens. One microliter equals 1,000,000 picoliters. The estimated volume of blood to transfer the Hepatitis B Virus is 10 picoliters and the estimated volume of blood to transfer the Hepatitis C Virus is 100 picoliters.

Therefore, the contaminated 19 samples of ejected fluid converts to 23,000 to 417,000 picoliters of blood, with the average volume of blood being 118,000 picoliters. This means these samples could hold 2,300 to 41,700 Hepatitis B virions and 230 to 4,170 Hepatitis C virions. With the averages being 11,800 Hepatitis B virions and 1,180 Hepatitis C virions. This data demonstrates blood-borne pathogens could have been transferred through the ejectate fluid of a Ped-O-Jet injector.

Second Test
In a second set of tests, the researchers assessed whether wiping the nozzle reduced or prevented cross-contamination between jet injections. The nozzle of the Ped-O-Jet was wiped with a cotton ball moistened in acetone immediately after inoculating the underside of a rabbit contaminated with 0.025 milliliters HBsAg serum. The Ped-O-Jet was then fired five times into five separate 1 dram vials. The ejectate fluid in each of the vials was assayed. This test was repeated ten times (Grabowsky et al., 1994).

Results found the ejected fluid of the next shot fired was positive for HBsAg in 3 out of 50 (6%) of the samples. Within these contaminated samples, the average volume of blood detected in the ejectate was 0.016 microliters (range, 0.01 uL – 0.022 uL) (Grabowsky et al., 1994). The exterior nozzle of the Ped-O-Jet was positive for HBsAg in 3 out of 10 (30%) of the samples. While the interior of the nozzle was again negative (0 out of 10) for HBsAg contamination (Weniger, 2003).

To put this into perspective, the contaminated 3 samples of ejected fluid converts to 10,000 to 22,000 picoliters of blood, with the average volume of blood being 16,000 picoliters. This means these samples could hold 1,000 to 2,200 Hepatitis B virions and 100 to 220 Hepatitis C virions. With the averages being 1,600 Hepatitis B virions and 160 Hepatitis C virions. The data demonstrates wiping the nozzle of the Ped-O-Jet reduced but did not eliminate contamination, and thus blood-borne pathogens could still have been transferred.

Limitations of Study
In reviewing this study, it came to the attention of this author that the researchers had failed to collect all of the data as planned within the original design of their study. After artificially contaminating the Ped-O-Jet, the gun was to be “shot” five consecutive times, each time into a 1 dram vial so the ejectate of the “shot” could be collected and assayed. Therefore the first “shot,” represents the first injection given after the jet injector became contaminated. The second, third, fourth and fifth shots represent the second, third, fourth and fifth persons to receive an injection after the jet injector became contaminated. This test was repeated ten times; thus creating 50 samples. However, Grabowsky and colleagues failed to assess and report how many of the HBsAg-positive samples were from the first shot, how many from the second shot, how many from the third shot, and so forth. The graph below demonstrates how the test should have been conducted. This data would be important in identifying how long the Ped-O-Jet remain contaminated, as was done within CDC’s 1977 evaluation.

Recommended Graph

For instance, in the first test 19 of the 50 samples were HBsAg-positive indicating that more than just the first shots were contaminated. We can presume that all ten of the first shots were positive and therefore either nine of the second shots tested were positive or eight of the second shots and one of the third shots were positive, etc. This information would have been very beneficial for assessing the degree of contamination.

Moreover, the data indicating the interior of the nozzle was negative for HBsAg contamination zero out of ten times is misleading. The experiment was repeated ten times. Therefore it can be assumed that the interior nozzle was only tested in each of the ten experiments after firing the fifth shot into the vial. Yet, as CDC’s 1977 experiment found, once the Ped-O-Jet became contaminated it remained contaminated for the following two consecutive shots. So the researchers should have analyzed within a third set of tests how many of the samples would be positive for HBsAg if the interior of the nozzle was tested after the first or second shots. Based upon the design of their study, they only assessed if the jet injector was still contaminated after firing five shots. The researchers failed to assess the risk to the next person in line once the jet injector became contaminated.

 

Mathematical Model
Grabowsky and colleagues (1994) also assessed the risk of blood-borne disease transmission via jet injectors and needle stick injuries by implementing a mathematical model. This equation is being thoroughly analyzed and scrutinized and will be reported upon at a later date.

From the Animal and Mathematical Models Grabowsky and colleagues summarized their findings. Join us Monday, September 18th to read Analyzing CDC’s 1994 Conclusion.

References:

  • (Grabowsky et al., 1994) Grabowsky M, Hadler SC, Chen RT, Bond WW, de Souza Brito G. Risk of transmission of hepatitis B virus or human immunodeficiency virus from jet injectors and from needles and syringes. Unpublished manuscript draft, dated January 3, 1994.
  • (Weniger, 2003) Weniger BG. Jet Injection of Vaccines: Overview and challenges for mass vaccination with jet injectors. Innovative Administration Systems for Vaccines (conference). Rockville, Maryland, USA, 18-19 December 2003.

 

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