Many serious and communicable diseases can be transmitted through the blood of an infected person. It is well known that viruses and bacteria are often carried in blood and can be passed on to others through contact with the contaminated blood. One such disease which can be spread by contact with a sample of blood carrying the virus is Acquired Immune Deficiency Syndrome, or AIDS, for which there is currently no cure. This disease has spread to significant proportions due to transmission of the virus through blood or other bodily fluids of infected persons.
Medical personnel are particularly susceptible to the spread of disease because of their frequent contact with the carriers of the disease. Syringes used to administer injections or remove bodily fluids for testing pose a substantial risk to doctors, nurses, and other medical personnel because of the chance of contact with the blood or bodily fluid and the possibility that the disease may enter the bloodstream of the medical technician through an exposed cut or abrasion or an accidental needle prick. Sanitation workers are also susceptible to accidental needle contact which can result in exposure to bacteria and viruses. For this reason, it is desirable that hypodermic syringes used to administer injections or extract bodily fluids for analysis and testing comprise a safety system so as to minimize accidental contact with the hypodermic needle and patient blood carried thereon.
In addition to inadvertent contact with infected blood, the spread of highly communicable diseases such as AIDS can be effected by re-use of the hypodermic needles and syringes described above. The needles are often sought by drug addicts to inject drugs intravenously into the blood stream. When used by drug addicts, the needles are often unclean and unsterilized, and thus, any virus or bacteria contained within residual blood or body fluids from the previous user is readily transmitted to the drug addict. The needles are often shared by the drug users, resulting in further spread of any bacteria or viruses contained in bodily fluids carried on the needles. Therefore, it is desirable to dispose of the syringes in a manner which prohibits their reuse.
Several syringes have been designed with protective elements in an attempt to minimize inadvertent needle contact and prevent reuse of the needle. One such syringe is shown in FIG. 1 of U.S. Pat. No. 4,820,272 entitled "Non-Reusable Hypodermic Syringe". The syringe comprises a cylinder having a series of inwardly extending grooves formed near the top end and a plunger having a mating series of outwardly extending grooves formed at the bottom end. These grooves allow the full insertion of the plunger within the cylinder but impede its withdrawal. French patent publication 2613628 discloses a similar type of syringe having flexible teeth formed in a piston which engage teeth in an outer tubular body to allow movement of the piston in one direction only. U.S. Pat. No. 4,731,068 entitled "Non-Reloadable Syringe" also discloses a syringe including means to prohibit retraction of the plunger once the contents of the syringe have been discharged.