Wenn Du den "abstract genau liest, dann steht da in der Einleitung:

A 2006 study from the United Kingdom found that penicillin use may decrease the risk of multiple sclerosis (MS).

Spaeter steht da zwar auch, wie von Dir richtig zitiert: "Penicillin use was associated with an increased risk of MS (odds ratio = 1.21, 95% confidence interval: 1.10, 1.27). "

Dann aber in der Schlussfolgerung: Thus, this study found that penicillin use and use of other antibiotics were similarly associated with increased risk of MS, suggesting that the underlying infections may be causally associated with MS.

Es wird also vielmehr vermutet, dass Infektionen mit MS zusammenhaengen koennen. Die Idee Penicillin VERURSACHT MS ist, zumindest diesem Artikel, nicht zu entnehmen. Man koennte hoechstens sagen, sie haben Ihre eigenen Daten falsch interpretiert.

Betr. Infektion und MS, siehe auch dieses C&P aus der englischen Wikipedia:

Infectious agents

Many microbes have been proposed as triggers of MS, but none have been confirmed.[2] Moving at an early age from one location in the world to another alters a person's subsequent risk of MS.[6] An explanation for this could be that some kind of infection, produced by a widespread microbe rather than a rare one, is related to the disease.[6] Proposed mechanisms include the hygiene hypothesis and the prevalence hypothesis. The hygiene hypothesis proposes that exposure to certain infectious agents early in life is protective, the disease being a response to a late encounter with such agents.[1] The prevalence hypothesis proposes that the disease is due to an infectious agent more common in regions where MS is common and where in most individuals it causes an ongoing infection without symptoms. Only in a few cases and after many years does it cause demyelination.[6][32] The hygiene hypothesis has received more support than the prevalence hypothesis.[6]
Evidence for a virus as a cause include: the presence of oligoclonal bands in the brain and cerebrospinal fluid of most people with MS, the association of several viruses with human demyelination encephalomyelitis, and the occurrence of demyelination in animals caused by some viral infection.[33] Human herpes viruses are a candidate group of viruses. Individuals having never been infected by the Epstein-Barr virus are at a reduced risk of getting MS, whereas those infected as young adults are at a greater risk than those having had it at a younger age.[1][6] Although some consider that this goes against the hygiene hypothesis, since the non-infected have probably experienced a more hygienic upbringing,[6] others believe that there is no contradiction, since it is a first encounter with the causative virus relatively late in life that is the trigger for the disease.[1] Other diseases that may be related include measles, mumps and rubella.[1]