in our place , people  throw syringes ( used for manily for insulin) in road side , i am scared that while walking through roadside , syringe may pierce into my foot. can it cause hiv infection??

Welcome to our Forum.  I will try to help.  Needle stick injuries are a potential source of HIV infection however, as suggested in your question, there are many types of needle stick injuries which effect the chance of becoming infected.  The most widely quoted figure is that if stuck with a needle which has been previously used by and HIV infected person, the risk for infection is about 0.32% (3 infections per 1000 needle sticks).  This calculation however is based on the concept that the needle stick occurs soon after it has been used on an HIV infected person such as in hospital settings.  Many factors can affect the risk for HIV infection with accidental needle sticks: 

Factors which increase the risk for HIV infection include:

1. If the person with HIV is untreated and has advanced disease.

2. The size of the needle since larger needles can, logically, transmit more blood,

3.  the presence of visible blood in or on the needle.

4.  Deep sticks which break the skin and cause bleeding.

Factors likely to decrease the risk for infection include:

1.  If the person with HIV is receiving treatment

2.  Smaller needles (insulin syringes are quite small).

3.  Superficial sticks which do not cause bleeding

4.  Increased time intervals between when the needle was used on an infected person and when the needle stick occurred.  HIV dies quickly at environmental temperatures and outside of the body.

For all of these reasons, the risk of acquiring HIV from accidently being stuck by a needle stepped on in the roadside is quite small, far less than 1%- most such needles have been used by persons who do not have HIV, the needles are small, and any virus present may not be infectious.  Despite all of these factors, most experts would advise efforts to avoid accidental needle sticks and consideration of HIV and hepatitis testing, as well as a tetanus shot should one be accidently stuck with a needle lying on the roadside.

I hope this information is helpful.  EWH

1) so, you are saying risk is small on roadside needle stick injuries . so there is no need to get scared ?

2) let me ask you one more thing, what about chances of getting hiv for hospital setting ??( for nurse and doctors) . i mean  what percentage of neddle stick injuries causes hiv infection in hospital setting ?

As I mentioned above, for doctors in nurses who get stuck with a needle which was previously used on a person with HIV, the risk for infection is also low, about 1 infectious for every 300'needle sticks, on average.  EWH