The S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) has staged an impressive rally over the past seven trading days, with the index managing to deliver investors a gain of around 5%.

Although the index has still lost around 3.9% for the year-to-date, the improved level of investor confidence has seen a number of shares rocket higher.

Three shares that are now trading at their all-time highs include:

1. NIB Holdings Limited (ASX: NHF) – NIB shares finally broke through the $4 level on Friday and last traded at $4.01 per share. The private health insurer has long been a top market performer, but its recent rally comes on the back of a better-than-expected earnings result. Top line revenue increased by an impressive 15.2% in an environment of subdued policyholder growth. Lower-than-expected claims inflation also helped to boost operating margins that resulted in an overall improvement in underlying earnings per share (EPS) of 10.6%. The shares aren’t in bargain territory anymore, trading on a forward multiple of more than 20x, so investors should think twice before rushing out to buy the shares at the current valuation.

2. Nanosonics Ltd. (ASX: NAN) For those investors who are unfamiliar with the company, Nanosonics develops decontamination and infection control products for the healthcare industry. The company’s target market is extremely large with infection control becoming increasingly important in hospitals around the world. Nanosonics already has a market capitalisation of more than $600 million – a huge valuation for a company that is yet to turn a profit from operations, but one that reflects the size of the company’s potential target market. Despite the company’s lack of profitability, it still remains in a financially strong position with more than $42 million in cash and minimal debt. Nanosonics certainly has the potential to be a global leader in infection control, but investors need to realise its lack of earnings makes it a very high-risk investment.

3. Iress Ltd (ASX: IRE) – IRESS shares hit an all time high of $11.18 last week after investors applauded the company’s full year FY15 results. The shares of the fintech company have now gained nearly 24% since the announcement that showed revenue and EPS growth of 10% and 9%, respectively. While these headline figures do not appear overly impressive, earnings momentum remains positive and investors are growing confident of stronger results in the year ahead as a number of recent acquisitions and new contracts make a full contribution to earnings. The company also has a number of international expansion opportunities that should drive earnings growth over the medium term. Despite these positives, it appears investors have already priced in this growth, with the shares now trading on a trailing price to earnings ratio of around 32. As a result, I believe investors should remain patient and look to pick up the shares on a more attractive valuation.

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Motley Fool contributor Christopher Georges has no position in any stocks mentioned. Unless otherwise noted, the author does not have a position in any stocks mentioned by the author in the comments below. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.